Potential Hurricanes and Flooding

Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu

We avoided most of the flooding seen in the Carolinas with Florence, but hurricane season lasts until the end of November. Some later planted corn is still drying down, so saturated soils and winds may cause lodging, but there are no hurricanes on the horizon that may cause those issues. Full season and double crop beans are more likely to have issues if another storm heads for the Delmarva. Depending on development stage, storm conditions could increase disease pressure, cause lodging and shattering. For more detailed information, check out NC State extension as they dealt with the aftermath of Florence (https://soybeans.ces.ncsu.edu/2018/09/soybean-considerations-following-hurricane-florence/)

For fields along tidal streams and shorelines, hurricanes could bring salt water across fields. It may be necessary to perform soil tests in these fields to check for salt levels prior to next year’s crop. In general, if Na makes up more than 15% of the cation exchange capacity, lower yields could be observed. Total salts (which can include Ca and Mg) may also cause issues in fields flooded with tidewater. Gypsum works well if Na is the only issue, but irrigation is needed to leach soils high in Ca, Mg and Na.

USDA Prepared to Respond to Hurricane Florence

WASHINGTON, Sept. 12, 2018 – The U.S. Department of Agriculture (USDA) reminds rural communities, farmers and ranchers, families and small businesses potentially impacted by Hurricane Florence of programs to provide assistance in the wake of disasters. USDA staff in the regional, State and county offices stand ready and eager to help. Additionally, USDA’s Operations Center will function around the clock.

“Our farmers and ranchers take financial risks every year to help feed and clothe the U.S. and the world, and a hurricane makes their situations even more perilous,” U.S. Secretary of Agriculture Sonny Perdue said. “At USDA, it’s our job to be there for them when they need help. All of our relevant agencies are ready to assist when natural disasters strike.”

USDA has important roles in both response to hurricanes and recovery efforts. USDA also is staffing the Regional Response Coordination Center in the Federal Emergency Management Agency’s (FEMA) Region IV, which covers eight states including North Carolina, South Carolina, and Georgia. USDA is providing 24-hour staffing to the FEMA National Response Coordination Center, and has personnel supporting the North Carolina and South Carolina State Emergency Operations Centers. USDA also is supporting FEMA Region II Regional Response Coordination Center in New Jersey to assist response efforts for Tropical Storm Isaac and Hurricane Florence. Additionally, personnel from the U.S. Forest Service and USDA Office of the Inspector General are pre-staging in Charlotte, North Carolina to assist with public safety and security efforts.

USDA recently launched a disaster assistance discovery tool through its new website Farmers.gov that walks producers through five questions to help them identify personalized results of which USDA disaster assistance programs can help them recover after a natural disaster.

In a continuing effort to serve the public, USDA also partnered with FEMA and other disaster-focused organizations and created the Disaster Resource Center website, located at www.usda.gov/topics/disaster. This central source of information utilizes a searchable knowledgebase of disaster-related resources powered by agents with subject matter expertise. The Disaster Resource Center website and web tool now provide an easy access point to find USDA disaster information and assistance.

USDA also encourages residents and small businesses in impact zones to contact USDA offices which meet their individual needs.

Food Safety and Food Assistance
Severe weather forecasts often present the possibility of power outages that could compromise the safety of stored food. The USDA Food Safety and Inspection Service (FSIS) recommends consumers take necessary steps before, during, and after a power outage to reduce food waste and minimize the risk of foodborne illness. FSIS offers tips for keeping frozen and refrigerated food safe and A Consumer’s Guide to Food Safety: Severe Storms and Hurricanes brochure that can be downloaded and printed for reference at home. Owners of meat and poultry producing businesses who have questions or concerns may contact the FSIS Small Plant Help Desk by phone at 1-877-FSIS-HELP (1-877-374-7435), by email at infosource@fsis.usda.gov, or 24/7 online at: www.fsis.usda.gov/wps/portal/fsis/topics/regulatory-compliance/svsp/sphelpdesk.

The USDA Food and Nutrition Service (FNS) coordinates with state, local and voluntary organizations to provide food for shelters and other mass feeding sites. Under certain circumstances, states also may request to operate a disaster household distribution program to distribute USDA Foods directly to households in need. As disaster response moves into the recovery phase, FNS may approve a state’s request to implement a Disaster Supplemental Nutrition Assistance Program (SNAP) when the President declares a major disaster for individual assistance under the Stafford Act in areas affected by a disaster. State agencies also may request a number of disaster-related waivers to help provide temporary assistance to impacted households already receiving SNAP benefits at the time of the disaster, and to provide flexibilities in administering school meals, the Special Supplemental Nutrition Program for Women, Infants, and Children, and other programs. Resources for disaster feeding partners as well as available FNS disaster nutrition assistance can be found on the FNS Disaster Assistance website.

Crop and Livestock Loss
The USDA Farm Service Agency (FSA) administers many safety-net programs to help producers recover from eligible losses, including the Livestock Indemnity Program, the Emergency Assistance for Livestock, Honeybees, and Farm-Raised Fish Program, Emergency Forest Restoration Program (PDF, 257 KB) and the Tree Assistance Program. The FSA Emergency Conservation Program provides funding and technical assistance for farmers and ranchers to rehabilitate farmland damaged by natural disasters. Producers located in counties that receive a primary or contiguous disaster designation are eligible for low-interest emergency loans to help them recover from production and physical losses. Compensation also is available to producers who purchased coverage through the Noninsured Crop Disaster Assistance Program, which protects non-insurable crops against natural disasters that result in lower yields, crop losses or prevented planting. USDA encourages farmers and ranchers to contact their local FSA office to learn what documents can help the local office expedite assistance, such as farm records, receipts and pictures of damages or losses.

Producers with coverage through the federal crop insurance program administered by the Risk Management Agency should contact their crop insurance agent. Those who purchased crop insurance will be paid for covered losses. Producers should report crop damage within 72 hours of damage discovery and follow up in writing within 15 days.

Community Recovery Resources
For declared natural disasters that lead to imminent threats to life and property, the USDA Natural Resources Conservation Service (NRCS) can assist local government sponsors with the cost of implementing recovery efforts like debris removal and streambank stabilization to address natural resource concerns and hazards through the Emergency Watershed Protection Program. NRCS had made available nearly $2 million in advance funding under the Emergency Watershed Protection program to help local communities immediately begin relieving imminent hazards to life and property caused by floods and is coordinating with state partners to complete damage assessments in preparation for sponsor assistance requests. NRCS also can help producers with damaged agricultural lands caused by natural disasters, such as floods.

The NRCS Environmental Quality Incentives Program (EQIP) provides financial assistance to repair and prevent excessive soil erosion that can result from high rainfall events and flooding. Conservation practices supported through EQIP protect the land and aid in recovery, can build the natural resource base, and might help mitigate loss in future events.

USDA National Institute of Food and Agriculture provides support for disaster education through the Extension Disaster Education Network (EDEN). EDEN is a collaborative multi-state effort with land-grant universities and Cooperative Extension Services across the country, using research-based education and resources to improve the delivery of services to citizens affected by disasters. EDEN’s goal is to improve the nation’s ability to mitigate, prepare for, prevent, respond to and recover from disasters. EDEN equips county-based Extension educators to share research-based resources in local disaster management and recovery efforts. The EDEN website offers a searchable database of Extension professionals, resources, member universities and disaster agency websites, education materials to help people deal with a wide range of hazards, and food and agricultural defense educational resources.

Many of USDA Rural Development programs can help provide financial relief to rural communities hit by natural disasters by offering low-interest loans to rural community facilities, rural businesses and cooperatives and to rural utilities. More information can be found on the Rural Development website, located at www.rd.usda.gov.

For complete details and eligibility requirements regarding USDA’s disaster assistance programs, contact a local USDA Service Center. More information about USDA disaster assistance, as well as other disaster resources, is available on the USDA Disaster Resource Center website, located at www.usda.gov/topics/disaster.

Variable Growth in Plasticulture Vegetables

Each year we see fields were vegetable growth in drip irrigated plastic mulched beds is irregular. While root diseases, nematodes, or soil insect feeding can cause variable growth, the following are other potential causes due to water quality problems, cultural practices, or irrigation system issues.

Plugged Emitters
Drip emitters can become plugged with fine particles, mineral deposits, or biofilms. When emitters become clogged, the plants nearest the clogs will receive less water and have more water stress and grow less or be stunted. This is seen most commonly in higher density planted crops such as peppers.

A common cause of plugged emitters is water containing high levels of dissolved iron. This often causes a proliferation of iron utilizing bacteria. These bacteria can form heavy biofilms on the inside of the drip tube. They also oxidize the iron in the water (as part of their metabolism) and leave behind iron precipitates that can plug emitters. Chlorination of drip lines is needed to control iron bacteria.

Another common problem in some aquifers, is well water with high levels of calcium and magnesium (“hard water”). In high water pH conditions, these can precipitate out as calcium or magnesium carbonates that will clog emitters. If you look inside the drip tubing you will see a white or chalky film. In addition, if soluble phosphorus fertilizers are put into water with high levels of dissolved calcium or magnesium salts, they can precipitate out as calcium or magnesium phosphates, also plugging emitters. Acidification of water can reduce or eliminate this problem. Also, avoid running phosphorus through the drip if you have hard water.

Inadequate filtering is another possible cause of plugged emitters. While this is most common when using surface water from ponds, ditches or streams it can also occur in wells that have fine particles in the water.

Pinched Drip Tape
Drip tape pinching will reduce water past the pinched area and result in poor growth. Pinched or folded tape often occurs near connections with lay flat hose, where tomato stakes have been installed directly over the drip tape, and in rocky or cloddy soils.

Improperly Designed or Maintained Drip Systems
Improperly designed drip systems can lead to over-watering or under-watering portions of the bed and cause variable crop growth. This most commonly occurs when systems are in too large of zones or have too small of supply lines, where pressure and volume is too low, or where length of run is too long. In these cases, the ends of the drip line will have much less water than the beginning of the run and will lead to a gradient of plant growth. Leaks in drip lines will also cause lower water delivery past the leak, leading to reduced plant growth.

Variable Depth of Planting and Transplant Handling
Many transplanted crops will show variability due to depth of planting. This is most common when the root ball is left partially exposed and dries out. If these plants survive they often will be stunted or will have reduced growth compared to plants around them. Planting too deep can also lead to variability in some plants. Rough handling or root ball disturbance can slow establishment of sensitive transplants leading to variability.

Variable Bed Formation
Variability in bed density and plastic laying can cause differences in plant growth. This is most common when plastic is laid in wet or cloddy soils. This results in variable bed densities affecting root growth and water movement and variability in plastic contact with the soil surface leading to warm and cool spots thus slowing or speeding plant growth.

Periods of heavy rain in June and now July causes local flooding in plasticulture fields where water covered over the top of beds and filled the bed through the planting holes. These areas will have poor growth due to lack of oxygen to the root systems and generally do not recover.

Vegetable Recovery from Temporary Flooding

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

On June 9, at our Georgetown research station, we received 4.2 inches of rainfall in a one-hour period. Many of our vegetable research plots were temporarily flooded and most of our plasticulture research area had water that topped the beds.

If this flooding would have lasted for more than 24 hours, most of our crops would have been lost. However, there was enough drainage early on so that the majority the area has come through, albeit with some complications. The following are some pictures that show the recovery and losses:

Pepper plants with leaf drop. Ethylene buildup in saturated soil conditions can cause leaf drop, flower drop, fruit drop, or early plant decline in many vegetable crops. The bed area around this plant was saturated for two weeks. For the plant to recover, the bed must dry out to allow the plant to regenerate roots. The pepper plant has additional sets of buds to allow for new leaves to form but the recovery, if it happens, will put the plant several weeks behind other non-affected plants. Another concern is potential for root rots. In severe cases, cutting away the plastic can save a crop by allowing for better drying out and aeration.

Watermelon plant in saturated bed conditions after flooding showing little growth. Oxygen starvation to vegetable roots will cause roots to cease to function resulting in plant stunting, or collapse, with limited recovery potential. For this plant to recover the bed must dry out and aerate enough for the plant to fully regenerate roots.

Flooded pickling cucumber planting. Soils in in this area stayed saturated for 3 days while seeds were germinating. Lack of oxygen caused seeds to deteriorate and plants did no emerger in much of the area.

Tomatoes fully recovered from temporary flooding. In this case the crop did not drop leaves and was able to regenerate new roots quickly.

Our watermelon variety trial stopped growing and aborted fruits after the flooding but has now fully recovered and plants are starting to fill in. The beds were allowed to dry out for 9 days after flooding and then the crop was fertigated with nitrogen and sulfur. New fruits are now being set but the trial will have few early watermelons.

Considerations for Controlling Weeds in Drowned Out Crops

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

An area of the field where the crop has drowned out gives weeds an opportunity to grow without crop competition, and potentially produce a tremendous amount of weed seeds. If a particularly troublesome species such as Texas panicum or Palmer amaranth is growing in these spots they could really cause problems for the next few years if they are allowed to produce seeds. So, what should you do? Some options to consider are whether you can reach these spots with equipment such as mower or sprayers; what crop is in the field; what you intend to plant in the field after harvest; and what will effectively control or kill the weeds?

Mowing is an option, but in all likelihood the areas will need to be mowed multiple times to prevent seed production.

If considering a herbicide, first assess the situation. If you are treating areas of a field, and will be harvesting the crop around the bare areas, you are limited to herbicide options for the crop planted in the field. Furthermore, you are limited to the same herbicide rates and herbicide application timings. Using herbicides with residual control is going to be important because you will not have a crop canopy present for later emerging weeds.

Also, consider what will be planted in the field next and check your rotational intervals. Will you have enough time between herbicide application and planting the next crop? This is a situation where you will have to assess each field individually, but these drowned out areas may need special attention.

Tackling the Nitrogen Dilemma in Corn

Management and Environmental Quality, University of Delaware, ashober@udel.edu, Sydney Riggi, Extension Agent – Nutrient Management, University of Delaware, sydney@udel.edu; Jarrod Miller, Extension Specialist – Agronomy, University of Delaware, jarrod@udel.edu; Phillip Sylvester, Extension Agent, University of Delaware, phillip@udel.edu; Karen Gartley, Soil Testing Program Director, University of Delaware, kgartley@udel.edu

As we have highlighted in previous weeks, managing nitrogen (N) when it won’t stop raining is a difficult task. The PSNT is meant to help measure the N that is available from organic amendments, like animal manures. Organic forms of nitrogen and ammonium are rapidly converted by soil microbes to nitrate (NO3) once soil temperatures exceed 60°F, conditions we have observed since late April/early May. As such, we expect that organic forms of N, like those in animal manures, were converted to ammonium (NH4+) earlier in the season. Once present as ammonium, conversion to nitrate by soil microbes is rapid (unless a nitrification inhibitor was applied to manure or soil). This nitrate was then susceptible to leaching below the root zone, runoff from fields where rainfall exceeded infiltration, or loss to the atmosphere from soils that were flooded for more than 48 hours.

We still advocate using a PSNT for fields with a recent history of manures or cover crops. However, the copious amounts of rain this year, coupled with rapid conversion of N in the soil, makes it difficult to rely solely on results of a PNST to determine your sidedress needs. Part of the difficulty we are having in making sidedress N recommendations this year is related to the huge variability in PSNT values we are seeing in fields with similar management. For example, we have received reports of pre-sidedress nitrate test (PSNT) values that are well below the 25 ppm NO3-N threshold (e.g., 8-10 ppm NO3-N) in soils that received moderate amounts of manure (e.g., 2-3 tons/ac) and commercial starter N fertilizers (30-80 lb/ac). However, we have also seen samples with PSNT values as high as 45 ppm NO3-N from nearby fields under the same management conditions. In a “normal year”, PSNT-based sidedress recommendations are determined by the concentration of nitrate in the PSNT sample, which is then adjusted for manure application (based on the timing and amount of manure applied) and any starter N applied prior to or at planting. But this year, Mother Nature is making it harder for us to make the call on if there is really manure N left to mineralize. We have also been measuring soil ammonium concentrations to look for evidence of delayed mineralization. Unfortunately, low soil ammonium concentrations (< 5 ppm) suggest that there is not much delay in the mineralization and that much of the organic N has been lost. As such, the University of Delaware Soil Testing Lab is recommending a range of sidedress N rates based on the PSNT.

Recognizing that N is important for adequate crop growth but that too much can result in environmental issues, we ask growers and consultants to consider the following before deciding exactly how much sidedress N to apply to corn (when you finally get out into the field):

  1. Are there visible signs of significant crop stress that will likely reduce the chance of achieving your expected yield goal (e.g., poor stand uniformity, dead or dying plants, poor root development) or does your corn look pretty healthy (e.g., even stand, healthy green color, healthy roots)?

If you have poor stand uniformity or signs that plants were drowned out, this is a good indication that you may lose yield. In this case, we recommend that you reduce your yield goal and fertilize at a lower N rate. Remember, fertilizing dead or dying corn will not bring it back. In contrast, if your crop looks to be in pretty good shape, then you can consider adding N at a higher sidedress rate to account for early season N losses.

  1. Will putting equipment into the field to sidedress cause more damage than it’s worth?

If you put equipment in the field while it is still too wet, you risk getting stuck and/or causing significant compaction. Both will cost you money and time to fix. If you can’t get equipment in the field before the corn is too tall, and you feel that you must get some N out, you have the option to fly on granular urea. While some sources recommend that you keep rates low (<60 lb/ac) to prevent leaf burn, research out the the University of Missouri suggests that applications of up to 150 lb/ac of urea are possible without significant leaf burn to the plant. If you do consider aerial urea application, you should consider that urea must be watered in (by rainfall or irrigation) to prevent significant ammonia volatilization; a urease inhibitor can help reduce ammonia loss, to some extent. The economics of aerial N applications should be considered before going this route.

  1. Can you fertigate?

If you are set up to fertigate and you can get your pivot around without causing compaction or getting stuck, we recommend putting out a modest amount of N now, then take tissue test later in the season and, if needed, add more N through the irrigation system later in the season.

  1. Will an additional N application cause you to add more than was in your nutrient management plan?

In Delaware, you should contact your consultant to have them write a justification for additional fertilizer applications. A copy of the addendum should be included with the original nutrient management plan before the end of the calendar year and will be essential if the farm is audited. The Delaware Department of Agriculture can be contacted for guidance and clarification. Consultants and growers from other states should contact State regulatory agencies for guidance. Click here for Delaware Department of Agriculture contact information.

Heavy Rainfall is Making Nitrogen Management a Challenge

Amy Shober, Extension Specialist – Nutrient Management and Environmental Quality, University of Delaware, ashober@udel.edu, Sydney Riggi, Extension Agent – Nutrient Management, University of Delaware, sydney@udel.edu; Gurpal Toor, Extension Specialist – Nutrient Management and Water Quality, University of Maryland College Park, gstoor@umd.edu; Bob Kratochvil, Extension Specialist – Agronomy, University of Maryland College Park, rkratoch@umd.edu; Jarrod Miller, Extension Specialist – Agronomy, University of Delaware, jarrod@udel.edu

Continued rainfall in our region has kept many growers out of the field again this week. These wet weather patterns are frustrating and serve as a reminder about the uncertainty and unpredictability of weather. Over the last four days, weather stations in Newark, Dover, and Georgetown report between 0.03 to 1.28 inches of rainfall and over the last month the Georgetown weather station has recorded 10.22 inches of rain. Not only has this excess rainfall affected the timely planting of corn (and even beans at this point), but has the potential to affect the crops that are already planted.

Nitrogen (N) management is one of the major challenges faced due to the wet conditions this spring. This type of wet weather is one of the main reasons we heavily advocate split applications of N to corn, despite the convenience of applying all N prior to or at planting. Early in the season, N uptake by corn will be about 1 lb of N per day per acre and N uptake will increase to approximately 3 lb N per day per acre during later vegetative stages. As such, if you applied 200 lb of N per acre prior to or at planting, uptake by the corn crop may be 30 lb per acre in the first 30 days; this leaves 170 lb of N per acre in the soil. This spring especially, N losses via leaching (movement of N below the root zone), runoff (movement of N in surface water flow), or denitrification (loss of N gas to the atmosphere) from fields that received all N prior to or at planting will be excessive, as shown in the below image.

In fields where only a small amount of N was applied prior to or at planting, the risk for early season N losses are reduced. This is because the bulk of the N is applied in a sidedress (or even one or more fertigation events) closer to the time that corn enters into rapid growth phase and the bulk of the N uptake occurs. The period of rapid N uptake occurs when corn is approximately 10 to 20 inches tall, which usually occurs sometime around 35 days after emergence. However, the N applied prior to sidedress, as well as residual N from past manure applications, cover crop biomass, or previous legume crops was susceptible to N losses this spring.

There is no way to know exactly how much N was lost from fields, as this requires precise measurement. While the extent of N loss will vary depending upon soil type, location, and amount of rainfall received, we can make some general assumptions about N losses. If we consider that 1 inch of rain adds 27,154 gallons of water to an acre and weighs about 113 tons, this 1 inch of rain will penetrate 6 to 15 inches in soil (depending on soil texture). This rain water will flush (leach) nitrate, which is the most common form of N in soils and is soluble and highly mobile (due to negative charge that prevents binding with soils), deeper into the soil profile. Since we received several inches of rain, we expect that nitrate has been leached below the current depth of plant roots. In addition, we have had several events where rainfall amounts exceeded the infiltration capacity of soils, resulting in ponding or even surface runoff. When runoff occurs, nitrate and N attached to soil particles is lost if you have erosion. In fields with ponding of water, conversion of nitrate to N gas, which will escape to the atmosphere, is highly likely.

Going forwards, growers should consider conducting a pre-sidedress nitrate test (PSNT) to determine if there is a need to add more N fertilizer. It is important to remember that the PSNT is most appropriate for fields where manure or other organic N sources were applied. Regardless of whether fields received all N up-front or a split application was planned all along, growers should contact their nutrient consultant to assure that in-season N application is in compliance with their nutrient management plan. As in season adjustments are made, Delaware nutrient consultants can write a justification for additional fertilizer applications. A copy of the addendum should be included with the original nutrient management plan before the end of the calendar year and will be essential if the farm is audited.

Tackling Drainage Issues for Vegetables and Agronomic Crops

James Adkins, Associate Scientist-Irrigation Engineering; adkins@udel.edu

The recent rainfall events have identified countless deficiencies in drainage across the region. While corrective measures are too late for many crops, there are some in-season options to help drain standing water and reduce disease potential.

Land Leveling
Leveling a field with a tool similar to a Rayne Plane or other land leveler prior to cropping can typically resolve minor puddling issues where the difference in elevation is 6 inches or less. If more than 6 inches of fill is needed this will not be a good option as too much top soil will be removed from the areas surrounding the depression and yield loss will occur. Land levelers are typically run on a diagonal to normal field operations and multiple passes may be required to achieve optimal results.

Surface Drainage
Most farms already utilize some form of surface drainage whether natural or manmade. Field operations including tillage and particularly laying beds for vegetable production often limit the natural flow paths for surface water. Trenches or periodic breaks in a vegetable bed should be put in place just after the beds are formed to allow water to escape as quickly as possible. After a major rain some shovel maintenance of the trenches will be necessary to maximize flow. Likewise, spinner ditches made with a rotary trencher or middle buster plow will likely require a shovel touchup if they have been crossed by a sprayer or planter. Swales or trenches with high flow rates and/or slope should employ a pipe, tile or stone at the outlet to minimize ditch bank erosion. Swales permit a much deeper flow path without the interruption to field operations however it may be necessary to seed the swale to grass to prevent gullying.

Tile Drainage
At this point most of the standing water is the result of a Delmarva Bay, or a deep depression in the middle of the field with no practical way to surface drain. Tile wells are the common solution that can be installed in the cropping season if the affected area is justifiably large. Inlets can be the traditional concrete type, slotted or perforated risers or a blind inlet consisting of stone and filter cloth that can be farmed across. The first step to determine if a tile well is a viable option is to assess whether there is an outlet with adequate elevation difference to successfully drain the depression. This is best determined with a transit, laser or gps survey equipment in coordination with the NRCS for survey and engineering support. For an initial assessment, Google Earth Pro (free download) has a feature where you can a draw a proposed flow path using the path measure tool and check the box labeled “show elevation profile” to view the elevation across the drawn path. https://www.google.com/earth/download/gep/agree.html

Ideally, the tile outlet in the ditch will have at least 1’ of free board above the normal ditch bottom level to prevent the tile line from silting closed and at least 0.1% grade (0.001 ft/ft or 1.2 in/100 ft of tile). Slopes as shallow as 0.02% can be accurately installed with laser and gps controlled tile machines but more slope is desirable to allow sediment to flush out of the tile. If the installation is done with an excavator or backhoe a minimum recommended grade of 0.1% should be followed. The tile should have a minimum of 2’ of cover at all times to prevent damage from equipment as plastic tile is easily crushed by tractors, combines and center pivot irrigation ruts.

While 4 inch flexible drain tile is often adequate in size to drain a small depression in a 12 – 24 hour period it is best suited for a plow installation and should not be trench installed due to its tendency to snake and rise above target grade during backfilling. Ideally 20’ sticks of 6 inch or larger dual wall pipe should be used in open trenches to help achieve target grade and prevent poor installation. When connecting multiple inlets into one tile line, it is preferable to tee into the mainline with a 6-10’ stub for each inlet to prevent a failed inlet from plugging the entire system. Whenever and open trench is dug, be sure to follow the proper safety procedures to prevent injury from trench collapse.

Pattern tiling is becoming more common on Delmarva and is an effective solution to address field that traditionally would be pattern ditched. Pattern tilling typically is used to dry and entire field that suffers from a high or perched water table that leaves the field saturated for extended periods and consists of parallel rows of slotted tile that must be installed with a plow or trencher.

Many folks have accepted pumping as their final solution. While I admit to using a transfer or irrigation pump to remove surface water in a pinch; the high volume of trash and sediment is very hard on seals and plastic impellers. It is preferable to use a trash or mud pump when available. A few Delmarva farmers, including the University of Delaware Warrington farm employ electric lift stations when an adequate surface drain for tile is unavailable. This option can be expensive but is often the only solution to difficult drainage situations on the shore.

For questions regarding the legality of installing any drainage system contact your local NRCS office.

For more information on tile systems and design the University of Minnesota has an extensive fact sheet. http://www.extension.umn.edu/agriculture/water/planning/planning-a-subsurface-drainage-system/

Weed Control After Recent Rains

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Rainfall over the past week have complicated weed control for fields planted before the rain. The rains have moved most of the herbicide out of the weed emergence zone and will there is probably not much left to provide residual control. With that said, we do not know if the herbicide is all gone, and thus replanting with something other than the original crop, may lead to crop injury.

So, be sure to visit your fields soon, and often, to look for new emergence and time your postemergence sprays before weeds get too large. Fields may need to be treated sooner than you normally would spray since herbicides providing residual control are probably gone.

Areas with drowned out crops may need to be replanted. Weed control in areas being replanted will be challenging. Be sure to start clean and kill any weeds that might be present. Consider if you will be able to get into these replanted areas later. If you are only replanting areas that were drowned out, it may mean that you will need to drive through taller corn to get to these spots. If that is the case, will you be able to get in there when the replanted sections need to be sprayed with postemergence herbicides. The earlier planted corn may be too tall to allow a sprayer to get in when the replanted corn is 10 to 14 inches tall. Therefore, you may need to think about relying more on residual herbicides with these replanted areas.

Drowned out areas that are not replanted should be sprayed to prevent weeds from getting established and ultimately producing seeds. Weeds growing in these areas can produce a tremendous amount of seeds that could cause problems for the next few years.

Flooding, Waterlogged Soils, and Effects on Vegetable Crops with Special Consideration for Plasticulture Vegetables

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

We have had widespread flooding in vegetable crops in May due to heavy and  extended rains. Soils in some field areas have remained waterlogged for several days. Over a 10-day period from May 12, 2018 at our Georgetown, Delaware Research station, 7.5 inches of rainfall fell. There were 4 days with rainfall over 1 inch and one day receiving 3 inches of rain. Many surrounding areas had over 10 inches of rain during this period.

Climate scientists predict that extreme weather events will become more common on Delmarva over the next several decades. This will present additional challenges for vegetable growers related to flooding, wet weather diseases, nutrient losses, ability to do timely harvests, field compaction, other wet soil issues, and resulting crop losses.

In 2018, initial plantings of watermelons and other fresh market vegetables have been made; peas are nearing harvest, and significant acres of pickles, snap beans, and sweet corn are in the field. Many processing vegetable fields have already had significant crop losses (sweet corn, snap beans, peas) due to flooding.

In flooded soils, the oxygen concentration drops to near zero within 24 hours because water replaces most of the air in the soil pore space. Oxygen diffuses much more slowly in water filled pores than in open pores. Roots need oxygen to respire and have normal cell activity. When any remaining oxygen is used up by the roots in flooded or waterlogged soils, they will cease to function normally. Therefore, mineral nutrient uptake and water uptake are reduced or stopped in flooded conditions (plants will often wilt in flooded conditions because roots have shut down). There is also a buildup of ethylene in flooded soils, the plant hormone that in excess amounts can cause leaf drop and premature senescence.

In general, if flooding or waterlogging lasts for less than 48 hours, most vegetable crops can recover. Longer periods will lead to high amounts of root death and lower chances of recovery.

While there has been limited research on flooding effects on vegetables, the following are some physiological effects that have been documented:

  • Oxygen starvation to vegetable roots will cause roots to cease to function resulting in plant collapse with limited recovery potential
  • Oxygen starvation in root crops such as potatoes will lead to cell death in tubers and storage roots. This will appear as dark or discolored areas in the tubers or roots. In carrots and other crops where the tap root is harvested, the tap root will often die leading to the formation of unmarketable fibrous roots.
  • Ethylene buildup in saturated soil conditions can cause leaf drop, flower drop, fruit drop, or early plant decline in many vegetable crops.
  • Leaching and denitrification losses of nitrogen and limited nitrogen uptake in flooded soils will lead to nitrogen deficiencies across most vegetable crops.
  • In bean crops, flooding or waterlogging has shown to decrease flower production and increase flower and young fruit abscission or abortion.
  • Lack of root function and movement of water and calcium in the plant can lead to calcium related disorders in plants. There is a potential for higher incidence of blossom end rot in tomatoes, peppers, watermelons, and other susceptible crops when fruits are forming and soils are saturated.

Low lying areas of fields are most affected by excess rainfall. However, cropping practices can also increase water standing. In vegetables, field compaction will reduce water infiltration leading to increased crop losses in wet weather.

Plasticulture Concerns in Wet Weather
In plasticulture, water can accumulate and persist between rows of plastic mulch because of the impervious surface of the mulch. Because much of the rainfall runs off the plastic, water pooling can be serious problem in plastic mulched fields, especially where row middles have become compacted. Vining crops that fruit into the row middles can have vines and fruits sitting in water and this produces ideal conditions for diseases of wet conditions to develop. A prime example is Phytophthora capsici (a water mold) that needs saturated soils or standing water to infect plants (fruits).

When water overflows the bed tops of plastic mulched crops, whole beds become saturated as water enters the planting holes. This often leads to plant losses as beds take a very long time to dry once saturated in this way and oxygen is very limited in the root zone.

To avoid water accumulation between plastic mulched beds, tilling with a deep shank or a subsoiler in row middles can help improve drainage. Cut drainage channels at row ends to reduce blockage (dams) that can back up water. Where practical, section plasticulture fields and install cross drains to remove extra water to improve drainage and reduce water damage potential. Growers may also choose not to plant lower areas in the field prone to water damage where plastic is laid.

In some crops such as peppers and strawberries, high raised beds will improve drainage significantly and can reduce losses to water standing between plastic rows. Another option in watermelons (and other strongly vining crops) grown on plastic is to reduce plastic bed width and increase distance between rows to limit impervious surfaces.

In some crops in our region (plasticulture strawberries for example), cover crops such as ryegrass are being grown between beds to reduce erosion. Research on row middle management will be a priority for the future.

Compaction between mulched beds can lead to increased ponding.

When water goes over top of beds they become saturated for long periods leading to plant losses. In this case the water just missed going over the bed (note the trash line).

Identifying Poorly Drained Areas for Phytophthora capsici Management
Growers with crops susceptible to Phytophthora capsici (P. cap) are encouraged to evaluate fields with susceptible crops (all vine crops, tomatoes, peppers, lima beans) for drainage issues where this disease can proliferate. The primary keys to P. cap management are limiting standing water, the potential for saturated soils, and water movement across the crop.

Recovering from Flooding or Waterlogging
One option to aid in vegetable crop recovery after floods or waterlogging is to aerate the soil by cultivating (in crops that can be cultivated) as soon as you can get back into the field. This allows for oxygen to enter the soil more rapidly. To address nitrogen leaching and denitrification losses, sidedress with 40-50 lbs of N where possible depending on the crop and crop stage.

In vegetable fields that remain wet, consider foliar applications of nutrients. Since nitrogen is the key nutrient to supply, spraying with urea ammonium nitrate (28 % N solution) alone can be helpful. These can be sprayed by aerial or ground application. Use 5 to 20 gallons of water per acre. The higher gallons per acre generally provide better coverage. As with all foliar applications, keep total salt concentrations to less than 3% solutions to avoid foliage burn.

Future Considerations
To address excess water challenges in the future, vegetable growers will need to invest in and plan for drainage in every field. Solutions including land levelling, surface drainage, tiles (tile wells, patterned tiling), and pumping may all need to be considered. See the article by James Adkins in this issue on drainage basics.

Row middles with ponding due to a field depression.