Spray to Prevent Late Blight on Potato and Tomato

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

Late blight has been found on potato in central New Jersey. The grower was applying preventative fungicides, however lesions occurred in a part of the field that the sprayer missed. All potato and tomato crops are susceptible to this disease. Growers should scout and apply preventative fungicides to protect their crops. Chlorothalonil, mancozeb or Polyram can be applied to potato and chlorothalonil, Gavel, or mancozeb can be applied to tomato. Complete coverage of the field is extremely important. Once late blight has been found close to a grower’s field, switch to a fungicide that is late blight specific. More information on available fungicides for this disease can be found at http://ag.udel.edu/extension/vegprogram/publications.htm#vegrecs.

Controlling late blight in organic systems is extremely difficult. Organic growers should apply a protectant such as copper to their crop. Serenade, Sonata and Sporatec are OMRI listed, and labeled for late blight. (However, there are very few research trials on efficacy of these products). It is critical to apply these materials with adequate coverage and at short spray intervals.

Spinach Foliar Diseases

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

Downy mildew of spinach has been found in the mid-Atlantic. This disease is not common in Maryland or Delaware, but I do see it occasionally. Symptoms begin with light spots on the upper surface of the leaf, followed by purple to grey fungal growth on the lower leaf surface (Figure 1).


Figure 1. Downy mildew sporulation on spinach leaves.

White rust (Albugo occidentalis) occurs more frequently in Maryland and Delaware. White rust symptoms begin with light green areas on the upper surface of the leaves. However in the case of white rust, the sporulation on the underside of the leaves is white, not grey (Figure 2). A third common spinach disease is anthracnose (Figure 3). Anthracnose is characterized by small tan lesions on leaves. Scout your spinach plantings and determine whether a disease is present. See the Commercial Vegetable Recommendation Guide for several effective fungicide options. Read the labels carefully because some fungicides applied at high temperatures may be phytotoxic, and many available and effective products, if used improperly, will result in resistance development. Alternate fungicide classes within a spray program, and follow resistance management guidelines on the label.

 Figure 2. White rust infected leaves with chlorotic (yellow) lesions on the upper surface and sporulation on the under surface.

Figure 3. Anthracnose lesions are tan nectrotic (dead) spots on spinach leaves.

Poor Stands or Stand Loss Due to Poor Seed or Plant Quality

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

As spring planting season continues at a rapid pace, there are more reports of poor stands or stand losses in vegetable crops. The culprits are often soil insects or diseases; however, poor quality seed or plants can also be a source of the problem. You will most commonly see problems with poor quality plants or seeds when there is a cold period right after planting.

As we progress into the warmer part of the planting season, it is often assumed that late spring and summer plantings will not have stand issues as soil temperatures are warm and seeds should germinate and emerge quickly and plants should root out quickly if there is adequate moisture. With seeds, this is not always the case, especially if seed lots are of low vigor. Signs of low vigor seed will be abnormal appearance in the bag (shrivelled, cracked, off color, misshapen), small seedlings that emerge late or do not emerge at all, abnormal growth (twisting, snaking, or corkscrewing), small shriveled cotyledons in beans, small or distorted true leaves, swollen or split hypocotyls or coleptiles, and bleached out seedlings. Another issue affecting seed germination and emergence would be uneven or inadequately applied seed treatments (fungicides and insecticides).

Seed companies do a very good job of producing quality seed and most seed is produced in drier areas where seed diseases are limited. Once seed is harvested it is conditioned, treated, packaged, and stored. As seed is distributed it often goes through several phases of where it is handled and stored in different environments. Larger lots may be broken in to smaller units and then repackaged by resellers. Once seed arrives at the grower it will be stored and handled again, finally making it to the planter. In each new storage and handling activity, there is potential to do damage to the seed. Rough handling, high temperatures, and high humidity are particularly damaging to seeds.

Poor quality plants can be due to diseases or other pest damage. There are however other causes of quality issues in plants such as being poorly hardened off, overwatered, stressed, over or under fertilized, overgrown or leggy, over mature, or root bound. Chemical phytotoxicity can be another problem. As with seeds, improper plant handing can lead to quality problems including overcrowding in greenhouse and holding areas, rough handing of trays, and storing in light limited conditions for extended periods. Breaking plant stems plants, especially those that with excessive growth, is a common problem in transplanting as is damage to roots when pulling plants out of trays.

When troubleshooting stand losses it is important to consider these issues affecting seed or plant quality.

Early Planted Lima Beans

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

Lima bean planting has begun in the region. With the expected warming trend, there is good potential for rapid germination and emergence this year due to higher soil temperatures. It is interesting to note that the variety Cypress was bred for good emergence under cooler planting conditions in Canada. We planted a trial using Cypress the first week in May this year and had excellent germination and emergence. We will harvest this trial the last week in July and then allow it to regrow and harvest a second time from the regrowth in October. Unfortunately, Cypress is very susceptible to pod drop due to heat. May planted lima beans, both at our research station and on growers farms in 2011 had very poor yields in the summer due to severe pod drop, even though some fields were well irrigated.

This illustrates the problem with May and early June planted lima beans: they most often have a lower yield potential than late June and early July plantings because they flower and set pods during summer conditions when day and night temperatures are high. Day temperatures greater than 90°F cause stomates to close early during the day to limit water loss, reducing lima bean photosynthesis. This results in fewer pods being carried by the plant. Night temperatures in the 70s or higher will also adversely affect yields because higher levels of carbohydrates are consumed in night respiration, limiting the plants ability to set and retain pods. Plants will reflower when cooler conditions recur, but this may lead to split sets.

Unfortunately, until more heat tolerant varieties are available (at the University of Delaware, one of our lima bean breeding objectives is to select for greater heat tolerance) , growers are limited in what they can do to maintain yields in early lima bean plantings. Fields closer to water bodies were temperatures are moderated by fog, heavy dew, high humidity, and cooling breezes during summer are the best candidates for early plantings. In addition, irrigate early planted fields, paying particular attention to the flowering and early pod set period and do not plant early lima beans dryland. Daytime irrigation can also help to moderate high temperature effects during hot summer periods. It is critical to keep early planted lima bean plants from being water stressed during this period.

Vegetable Crop Insects – May 25, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Cucumbers
Be sure to scout for cucumber beetles and aphids. Fresh market cucumbers are susceptible to bacterial wilt, so treatments should be applied before beetles feed extensively on cotyledons and first true leaves. Although pickling cucumbers have a tolerance to wilt, a treatment may still be needed for machine-harvested pickling cucumbers when 5% of plants are infested with beetles and/or plants are showing fresh feeding injury. A treatment should be applied for aphids if 10 to 20 percent of the plants are infested with aphids with 5 or more aphids per leaf.

Melons
Continue to scout all melons for aphids, cucumber beetles, and spider mites. The treatment threshold for aphids is 20% infested plants with at least 5 aphids per leaf. The first spider mites are being found in watermelons. The threshold for mites is 20-30% infested crowns with 1-2 mites per leaf. We have also seen an increase in cucumber beetle activity, especially in cantaloupe fields. Since beetles can continue to re-infest fields as well as hide under the plastic, be sure to scout carefully for beetles both under the plastic and on plants. With the predicted hot weather this weekend, we could see a rapid increase in populations.

Potatoes
Fields should be scouted for Colorado potato beetle (CPB), corn borers (ECB) and leafhoppers. Adult CPB as well as the first small larvae can now be found in fields not treated at planting. A treatment should be considered for adults when you find 25 beetles per 50 plants and defoliation has reached the 10% level. Once larvae are detected, the threshold is 4 small larvae per plant or 1.5 large larvae per plant. As a general guideline, controls should be applied for leafhoppers if you find 0.5 to 1 adult per sweep and/or one nymph per every 10 leaves.

Snap Beans
Continue to sample all seedling stage fields for leafhopper and thrips activity. The thrips threshold is 5-6 per leaflet and the leafhopper threshold is 5 per sweep. If both insects are present, the threshold for each should be reduced by 1/3. Once corn borer catches reach 2 per night, fresh market and processing snap beans in the bud to pin stages should be sprayed for corn borer. Sprays will be needed at the bud and pin stages on processing beans. Once pins are present on fresh market snap beans and corn borer trap catches are above 2 per night, a 7 to 10-day schedule should be maintained for corn borer control. (http://ag.udel.edu/extension/IPM/traps/latestblt.html).

Sweet Corn
We have received reports of an increase in wireworm damage, especially in fields where damage has occurred in past years. Although most, if not all seed is treated with one of the commercial applied neonicotinoid seed treatments, a soil insecticide may also be needed in fields with heavy population pressure. Once fields emerge, be sure to sample for cutworms and flea beetles. You should also sample all whorl stage corn for corn borers. A treatment should be applied if 15% of the plants are infested. The first silk sprays will be needed for corn earworm as soon as ear shanks are visible. Be sure to check trap catches since the spray schedules can quickly change. You can call the Crop Pest Hotline for the most recent trap catches (in state: 1-800-345-7544; out of state: 302-831-8851) or check our website at http://ag.udel.edu/extension/IPM/traps/latestblt.html.

Grain Marketing Highlights

Carl German, Extension Crops Marketing Specialist; clgerman@udel.edu

Weekly Crop Progress 05/13
U.S. corn planting was reported to be 87 percent complete with 56 percent emerged as of Sunday May 13. U.S. soybean planting was 46 percent complete and 19 percent emerged. Winter wheat was 72 percent headed with overall conditions in much better shape than last year. Spring wheat and barley were also reported to be well ahead of the five year average for planting and emergence.

USDA Export Sales Report 05/17
Pre-report estimates for the week ending May 10 placed weekly corn export sales at 31.5 to 55.1 million bushels. Total export sales for the week were recorded at 34.1 million bushels with 13.4 million scheduled for the current marketing year. This was above the 13.1 million bushels needed this week to stay on pace with USDA’s export projection of 1.7 billion bushels. Weekly shipments of 26.2 million bushels were below the 35.5 million bushels needed this week. This report is viewed as slightly bearish.

Pre-report estimates for weekly export sales of soybeans ranged from 40.4 to 58.8 million bushels. Total export sales were reported at 24.7 million bushels with 22.6 million scheduled for ‘11/‘12. This was well above the 2.8 million bushels needed this week to stay on pace with USDA’s export demand projection of 1.315 billion bushels. Shipments of 20.9 million bushels were well above the 13.8 million bushels needed this week. This report is viewed as bullish.

Pre-report estimates for wheat exports ranged from 14.7 to 29.4 million bushels. Total export sales were reported at 26.1 million bushels with 11.8 million bushels scheduled for the current year. This was above the 3.6 million bushels needed this week to stay on pace with USDA’s demand projection of 1.025 billion bushels. Weekly shipments of 24.9 million bushels were below the 33.9 million bushels needed this week. This report is viewed as bearish.

Market Strategy
The U.S. wheat harvest is expected to begin at least two to three weeks early this year paving the way for the likelihood that more acres will go to double crop soybeans, possibly increasing 2012 U.S. soybean acreage by another 2 million acres (+ or -). Even so, old crop and new crop soybean supplies will remain at tight levels.

The commodity markets continue to grind along as the 2012 growing season gets well underway. The recent sell-off created buying opportunities for commercial and non-commercial traders in the near term. China was rumored to have made large purchases of U.S. corn and soybeans this week coming on the back of slightly bearish corn and bullish soybean sales for the week ending May 13. For the moment this was fundamentally price supportive.

The equities markets are experiencing a backlash from the EU with major resistance getting in the way of needed financial reforms. It remains to be seen whether the Euro remains intact. World equity and commodity markets will be impacted by the outcome. The U.S. dollar has strengthened every day for the past two weeks as a result of the ongoing uncertainty in the European Union.

The new crop corn price has recovered about 20 cents per bushel from the low of last week’s sell-off. New crop SRW wheat has rebounded about 40 cents per bushel. New crop soybeans are only showing a single digit gain. Uncertainty abounds. Currently, Dec ‘12 corn futures are trading at $5.28; Nov ‘12 soybeans at $13.09; and July SRW wheat at $6.41 per bushel.

For technical assistance on making grain marketing decisions contact Carl L. German, Extension Crops Marketing Specialist.

Agronomic Crop Insects

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Alfalfa
Potato leafhoppers are now present in fields so be sure to sample on a weekly basis after the first cutting. Once the damage is found, yield loss has already occurred. The treatment thresholds are 20 per 100 sweeps on alfalfa 3 inches or less in height, 50 per 100 sweeps in 4-6 inch tall alfalfa and 100 per 100 sweeps in 7-11 inch tall alfalfa.

Field Corn
During the past week, we have seen an increase in the number of no-till fields with economic damage from cutworms. Damage has mainly occurred in fields that were not treated with a cutworm product at planting. Be sure to scout fields carefully for cutworms – in some cases you will need to check fields twice a week to be sure you do not miss an economic population. In addition to cut plants, be sure to watch for leaf feeding which can be an indication of the potential for significant cutting damage and yield loss.

Slugs continue to be a problem in later planted fields. In fields where Deadline MPs have been applied at a rate of 10 lbs. per acre and the distribution of pellets is at 5 per square foot, control has been very good. The best control with the Deadline M-Ps (up to 2 weeks in some cases) has been observed when applications were made and there was at least one day of sunny weather after an application.

Small Grains
We continue to find armyworms and cereal leaf beetles in barley and wheat fields that were not treated. Population levels remain variable throughout the state so scouting fields will be the only way to determine if an economic level is present. Although armyworm can attack both wheat and barley, they can quickly cause significant losses in barley. Heavy defoliation of the flag leaf can result in significant economic loss. Armyworms generally begin head clipping when all vegetation is consumed and the last succulent part of the plant is the stem just below the grain head. Larvae can feed on the kernel tips of the wheat, resulting in premature ripening and lower test weight.

As barley and wheat approach harvest, the treatment options change due to the pre-harvest interval (the waiting period between application and harvest). In addition, not all materials are labeled on both crops so be sure to carefully read all labels – remember the label is the law.

Soybeans
As the earliest beans emerge, be sure to watch carefully for slug damage. Remember, if you had a problem in past years, the slugs may still be present in fields and can quickly damage soybeans if present as plants emerge. Be sure to also watch fields carefully for bean leaf beetles and grasshoppers. Small grasshoppers have already been detected in fields before planting. Early detection and control of small grasshoppers is necessary to achieve control. As a reminder, OP insecticides (examples – dimethoate or Lorsban) cannot be combined with SU/ALS herbicides. Since other materials may also state restrictions regarding combinations of insecticide and herbicides, you should be sure to check all labels carefully before combining insecticides and herbicides.