Sanitation is Important in Transplant Production Houses

Jerry Brust, IPM Vegetable Specialist, University of Maryland;

By now almost all growers have started transplant production or have hired someone else to grow their transplants. With all of the important things that go into transplant production one of the sanitation factors that is somewhat neglected is weed control. Figure 1 shows the outside edge of a high tunnel production house in February. The grower was getting ready to drop seed in just a few days after they cleaned up the house from the fall growing season. This particular grower had been having intermittent problems with thrips (and consequently tomato spotted wilt virus) and two spotted spider mites in their production house. The chickweed you see on the outside and more on the inside at the base of the high tunnel was harboring a few thrips and a few mites. All the thrips and mite holdovers from the fall were female and would be ready to feed and lay eggs in the next week. The grower was cleaning up the weeds and debris from last fall five days before they were to start their seedling trays. This is not enough time to eliminate the pest problems that were on the overwintering weeds. Three and probably four weeks would have been much better to greatly reduce the mite and thrips populations. Not only can chickweed harbor these two major insect and mite pests, but the weed also can act as a host for tomato spotted wilt virus along with other weeds such as Canada thistle, ragweed, redroot pigweed, nightshade, chicory, yellow sweet and white clovers, phlox and many others. This makes it imperative that growers control their weeds weeks, if not months, before they drop seed for their vegetable or flower transplants. This includes controlling the weeds throughout the production period. Often times growers become very busy this time of season and neglect managing new weed problems as they arise (Fig. 2). I know we are always asking you to control your weeds in your vegetable fields, which is a difficult thing to do, but it is much more manageable to control weeds in a high tunnel or greenhouse over a period of a few months.

Figure 1. Chickweed present inside and outside a high tunnel being prepared for transplant production

Figure 2. Weeds growing alongside transplants

Besides insects and viruses weeds also can harbor fungal and bacterial diseases. One of the worst diseases and one that is becoming much more of a consistent problem in our tomato fields is bacterial spot caused by four species of Xanthomonas (Fig. 3). I think part of the reason bacterial spot has become such a problem is that it establishes itself in the field early in the season. This may be due to several factors such as weeds in the field harboring bacterial spot disease, Xanthomonas strains with copper resistance and by transplants being infected. Transplants can become non symptomatic carriers of bacterial spot. Studies have found that a tray with one seedling that is infected can result in several plants in that tray and surrounding trays having Xanthomonas spp. bacteria on them but with no infection. It would be impossible to know which plants were carriers and which were not. Bacterial spot is so prolific a disease that one infected seed in 10,000 can start an epidemic in the field. To help reduce any chance of bacterial spot in your transplants, good sanitation practices need to be used in the production area and seeds should be hot-water treated, which will eliminate the bacteria from the surface of the seed and more importantly from within the seed.

Figure3. Bacterial spot on a tomato leaf



Pollenizer Systems and Spacing for Seedless Watermelon Revisited

Gordon Johnson, Extension Vegetable & Fruit Specialist;

There are four pollinizer systems that have been successful for seedless watermelons. The original research with seedless production showed that for standard size seedless watermelons a 1:3 ratio of pollenizers to seedless maximized yields and field space. A 1:2 ratio did not increase yield. A 1:4 ratio gave similar results often to a 1:3 ratio. However, if there were any pollinizer losses, the reduction in pollen production had a much greater yield effect. For example, a 20% pollinizer loss in a 1:3 ratio results in a final ratio of about 1:3.8; in contrast, a 20% pollinizer loss in a 1:4 ratio results in a final ratio of 1:5 which can be pollen limiting.

Pollenizers can be planted in several configurations:

  1. Pollenizers are planted in separate rows between seedless rows
  2. Pollenizers are planted every fourth plant in the seedless row at even spacings
  3. Evenly spaced seedless plants with the pollinizer placed between every third and fourth seedless plant in-row
  4. Every third plant is co-planted with seedless and pollenizer in the tray and then planted in-row

Research has shown that the in-row pollinizer planting method (3) and the co-planted pollenizer method (4) have the highest yield potential per area planted.

One issue with in-row pollenizer planting is the need to have a separate pollinizer planting operation at the same time the seedless is being planted. This has led to problems with mixing up pollenizers and seedless plants by planting crews. One way that this can be avoided is by spraying a white particle film clay product on the pollenizers to “color code” them so that crews can tell them apart from the seedless. Research at UD has shown that this coating has no effect on pollinizer performance as new leaves that are produced are normal green in color.

Another way that this issue has been addressed is to switch to co-planted pollenizers. In this program, every third plant double planted with a seedless and a pollinizer plant. The planting crew then pulls plants in order from the tray and the correct ratio (1:3) of pollinizer to seedless is planted without needing a separate planting operation. This eliminates the need for separate planting trays of pollenizers to keep track of and reduces by ¼ the number of trays to be carried in the field.

With seedless spacing, research has shown that with standard seedless types (36-60 count seedless), a 3-foot spacing between plants give the best yield and economy (plants used). Closer spacing had the potential for higher yield but did not justify the higher plant cost while wider spacing (4 ft. between plants or greater) sometimes reduced yield or increased hollow heart.

In mini-watermelons (under 8 lbs), the standard recommendation hast been to plant at a 2 ft spacing between plants. However, other research has shown that yield and size grades were optimized at a 1 ft in-row spacing.

Research on pollenizers for seedless watermelon production in several production regions including Delmarva, Georgia, and Indiana have shown some interesting results. The bottom line is that pollenizer selection can be as important for overall yield, fruit quality, and early crown set as the triploid seedless variety selected.

Research at the University of Delaware and the University of Georgia showed that early flowering differed with pollenizers and seedless varieties and that some combinations were better matched than others.

An interesting point to consider is that currently, no one pollenizer is perfect for achieving high early sets, high later sets, reduced hollow heart, and total over all yields. In addition, some standard seeded and special pollenizers are better suited for in-row use than others.

The following are some points on how to get achieve the best results for seedless watermelon production with pollenizer choice:

  • For in-row and co-planted systems, choose only those pollenizers that provide good male flower production but that are not overly competitive. Most special pollenizers work well, but fewer standard seeded types are adapted to these uses (Stargazer, Mickylee, hybrid icebox types). In contrast, the more vigorous seeded types are well suited for separate bed systems (such as Sangria, Estrella).
  • Advances have been made with special pollenizer breeding and newer generation pollenizers have better disease packages and more extended flowering. If one pollenizer is being used, consider these new varieties (SP-7 from Syngenta or Wild Card Plus from Sakata as examples).
  • Consider using two pollenizers in a field. Choose a good early flowering type for effective early yield and long flowering type for sustained yield. Field surveys have shown good results where this type of combination has been used.

In fields where diseases are a concern such as second year fields, or those that have had shorter rotations, use only pollenizers with good disease resistance packages. For example, research in Indiana has shown that some pollenizers are much more susceptible to anthracnose and Fusarium wilt than others.

Overhead Irrigation of Vegetable Crops – Irrigate to Insure Even Emergence, Understanding Water Use

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Irrigation is a critical management tool for producing high yielding and high-quality vegetable crops. Direct seeded vegetables such as peas, lima beans, sweet corn, spinach, cucumbers, and snap beans require adequate soil moisture and certain soil temperature optimums to germinate and emerge. If soils are dry at planting, irrigation will be required to assure rapid and even emergence. This is particularly critical for processing vegetables where delays in emergence can cause lengthened times to maturity, affecting harvest timing. Irregular emergence in dry soils can also lead to difficulties in processing crop harvest scheduling due to variable maturities in the field.

Sandy loam soils need about a half inch of irrigation to wet the soil down to 6 inches to insure germination until the next rain. Heavier loam soils may need 0.7 inches to 0.9 inches of water to wet the top 6 inches of soil.

In extremely dry soils, such as planting no-till into a burn-down rye cover crop, irrigation water should be applied prior to planting to improve planter performance and seed germination. Fields with heavy cover crop also may require irrigation prior to burndown and planting

Having the irrigation system ready to run when you plant can make the difference between a good stand with maximum yield potential or having a poor or variable stand with lower yield potential.

Scheduling irrigation for different vegetables grown under center pivot, travelling gun, or solid set overhead systems involves knowledge of the soil water holding capacity, the effective rooting depth of the crop (how deep water can be drawn by the crop), how efficiently water is being delivered (water losses to evaporation before it reaches the crop and how much water is lost to runoff), how much water is being used by the crop (transpiration) and how much water is being lost from the soil and wetted surfaces directly (evaporation). The combination of transpiration and evaporation losses is termed evapotranspiration.

To schedule irrigation, the goal is to replace water lost through evapotranspiration without excessive runoff or excessive loss through percolation out of the root zone. Another factor to consider is the permissible water depletion; how much will you allow the soil to dry down between irrigations. For most crops we set this at 50% of the water holding capacity of the soil. However, for some shallow rooted crops you may want to keep that value lower (only allow for 30% depletion between irrigations). By knowing how much water is being lost and how much is left in the soil, you can determine when to irrigate and how much to irrigate.

Vegetable Crop Insect Scouting

David Owens, Extension Entomologist,

Asparagus is emerging from the soil and air temperatures have been favorable for insect activity. Be on the lookout for asparagus beetle. If 5-10% of spears are infested with adults, or 2% of spears with eggs, treatment may be advised. Please refer to the Mid-Atlantic Vegetable Production Recommendations for treatment options if necessary, which can be found here:

Imported Cabbageworm adults are active (see the Guess the Pest answer in this edition from last week’s challenge). Begin scouting for worm activity.

Using Degree Days to Predict Insect Life Cycles

David Owens, Extension Entomologist,

Because insects generally have limited mechanisms of regulating their temperature, insect development and life history is tied to ambient temperature. This enables certain life history events to be predicted fairly accurately. The easiest way to calculate degree days is DD = (max temp + min temp)/2 – Insect base temperature. A negative number counts as a 0. For example, seedcorn maggot’s base temperature is 39, if a day’s high was 50, low 30 then DD = (50+30)/2 – 39 = 1. This week in Georgetown, we hit peak overwintering seedcorn maggot adult activity (base 39, DD target 360, start Jan 1). Fields with recent manure incorporation may have maggot eggs in them. Other insects of interest are as follows:

Alfalfa weevil DD = 200–300, base 48°F.

San Jose scale DD = 380, base 51°F. Start sampling at DD 300. Maximum crawler activity DD 600.

Cereal leaf beetle egg lay DD = 327, base 46°F.

Spring Cover Crops for Vegetable Rotations

Gordon Johnson, Extension Vegetable & Fruit Specialist;

One principle of managing soil for improved health is to always have a crop growing on the soil. This will maintain or add organic matter, provide benefits from the action of growing roots, and recycle nutrients.

Where fall cover crops were not planted due to late harvest, spring cover crops can be planted in early April to provide soil health benefits where vegetables and field crops are not scheduled until late May or the month of June.

The most common cover crop options for late March or early April planting include spring oats, mustards and annual ryegrass. Plant oats at 90-120 lbs per acre, mustards at 10-20 lbs per acre, and annual ryegrass at 20-30 lbs per acre.

Field peas are another option; however, we are somewhat south of the best zone for spring planting. One type of field pea is the winter pea which is often fall planted in our area but can be spring planted. It has smaller seed so the seeding rate is 30-60 lbs per acre. Canadian or spring field peas are larger seeded and used as a spring cover crop planted alone at 120-140 lb/A.

Mixtures can also be used. Field peas are well adapted to mixing with spring oats or with annual ryegrass. Reduce seeding rates of each component when using in mixtures. Recommended seeding rates are 70 lbs of oats per acre and 40 lbs/A of Austrian winter peas or 80 lbs/A of Canadian or spring field peas.

Many mustard family crops have biofumigation potential. When allowed to grow to early flower stage and then incorporated into the soil, they release compounds that act as natural fumigants, reducing soil borne disease organisms. Some biofumigant mustard varieties and blends include ‘Pacific Gold’, ‘Idagold’, ‘Caliente’, ‘Trifecta’, and ‘Kodiak’. Other mustard family crops serve as non-hosts, trap crops, or deterrents for pests. In research at the University of Delaware biofumigation using early spring planted biofumigant crops such as ‘Image’ radish, ‘Dwarf Essex’ rapeseed, or ‘Nemat’ arugula showed potential for managing root knot nematode populations. When used as a biofumigant, mustard family cover crops should be grown to achieve maximum biomass by adding 60-100 lbs of nitrogen per acre. Nitrogen is also required to produce high biomass with spring oats and annual ryegrass at similar rates. When planting mixtures with peas, nitrogen rates should be reduced.

An often-forgotten spring seeded legume crop that can also be used is red clover. Red clover can be frost seeded into small grains, seeded alone, or mixed with spring oats or annual ryegrass. Seeding rates for pure stands would be 10-16 lbs/A, for mixtures 6-10 lbs/A.

Spring planted radishes and mustards as cover crops.

Pea Herbicides

Mark VanGessel, Extension Weed Specialist;

Weed control options remain limited for processing peas. Pursuit can be used as a pre-plant incorporated or preemergence treatment and is used primarily for broadleaf weeds. Preemergence applications of Command or Dual are labeled for control of annual grasses and some broadleaf weeds. Crop safety with these herbicides improve as the air and soil temperatures increase.

Be aware that if you intend to plant lima beans after peas, Command cannot be used in peas. The Command label states a 9-month rotation between application and planting lima beans

For postemergence applications, Basagran and Thistrol are labeled for broadleaf weeds. Apply Basagran after peas have more than three pairs of leaves. Do not add oil concentrate. Select, Assure II, Targa, or Poast can be used for postemergence grass control.

For no-till plantings of early peas, controlling all weeds present before planting can be challenging. The cool weather can result in poor performance with glyphosate. There are no products that can be tankmixed with glyphosate to improve control in this situation. In some situations, use of glyphosate 10 to 14 days prior to planting and then a sequential application of Gramoxone maybe need at planting to completely kill weeds prior to planting.

Recent Vegetable Trends

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Vegetable growers that direct market or that target marketing programs to entice buyers should be on the leading edge of food trends.

Food trends are driven by many factors such as health benefits, dietary shifts, public values, celebrity recognition, and customer diversity.

The great thing about food trends is that you, as a grower and marketer, can help to start trends, invent new ways to market your produce, develop tastes in your customer base, and help define new eating habits.

One of my goals as a vegetable specialist located in Delaware is to reinvent one of our most important regional crops, the lima bean, by promoting different specialty types. We have been testing a range of potential specialty lima beans from our breeding program and other diverse sources that have different sizes, shapes and colors for cooking, eating, and taste attributes.

In recent years other vegetable trends have waxed and waned. The word on the street is that kale’s best days are now behind it. However, Brussels sprouts are still going strong, cauliflower is being put into everything, arugula is still hanging in there, and beets are on the upswing (2018 was the year of the beet).

Beets are an interesting study in trendiness. Five years ago, you would see small sections of beets in the fresh, canned, pickled, and frozen sections of the supermarket, maybe 10 selections at most. Now there are beet products in the juice, snack, and health product sections. Why? Because beets are being promoted by the “health” industry as a superfood.

A current question that is being asked by trend analysts is what will replace kale in the “greens” arena. One group that is gaining traction is chard and beet greens. Chard is now being sought by chefs as the new greens item to add menu selections. Other trend followers suggest that “wild” tasting plants will be part of the new trend driven by chefs. This includes sorrel, dandelion, an amaranth.

There are dozens of types of dandelions from the common weed to cultivated types. All parts of the weedy dandelion can be used as food and as a medicinal. Dandelion greens are very nutritious and can be added to salad and soups or cooked as a greens side dish. I expect to see some growers start to provide this as an actual crop. It is also perennial.

Edible amaranth is close relative to pigweed and makes a rich flavored cooked green. It is very easily grown and loves the summer heat. In addition to this new trend, it is a favorite of many immigrants from the Caribbean and Africa.

Sorrel is lemony flavored and there are selections that have been made for specific leaf attributes. It is this flavor that has brought it back to the table. Expect to see it more on plates in the future.

Other interesting trends include:

Vegetable “steaks” – these are vegetables that can be sliced and grilled like steaks (eggplant, squashes, tomatoes). This is a new way to market “old” crops.

Small sizes – small versions of popular vegetables. Snack peppers, snack cucumbers, mini eggplants, mini squashes and much more are becoming more and more popular. This follows the past baby vegetable trend but with new crops.

Color and color blends – Colorful vegetables are very trendy, especially in blends or mixtures. Everything from chard to cauliflower, carrots to peppers.

Fermentable foods – Grow foods for your customers to ferment. Cabbage, Napa, Pak choy, daikon, cucumbers, peppers, and many more.

Ugly produce – Off shapes and types are now sought. An example would be the ugly tomato that has been marketed as such in grocery stores.

2018 University of Delaware Spring and Fall Beet Trials

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Spring and Fall beet variety trials were conducted in 2018 at the University of Delaware research farm near Georgetown, DE.

Varieties Evaluated and Sources

Variety Source Type
3×5 D&D Seed Co Red Globe F1
3×11 D&D Seed Co Red Globe F1
Avalanche Bejo Seeds White Globe OP
Bohan Bejo Seeds Red Globe F1
Boldor Bejo Seeds Yellow Globe OP
Boro Bejo Seeds Red Globe F1
Bresko Bejo Seeds Red Globe F1
Falcon Sakata Red Globe F1
Kestrel Sakata Red Globe F1
Manolo Bejo Seeds Red Globe F1
Merlin Sakata Red Globe F1
Moneta Bejo Seeds Red Globe OP
Pablo Bejo Seeds Red Globe F1
Red Ace Sakata Red Globe F1
Red Atlas D&D Seed Co Red Globe F1
Red Cloud Bejo Seeds Red Globe F1
Red Kite Sakata Red Globe F1
Red Titan D&D Seed Co Red Globe F1
Soldier Bejo Seeds Red Globe OP, Red Foliage
Taunus Bejo Seeds Red Elongated F1


Materials and Methods
There were 20 beet varieties entered and planted in both a spring and a fall trial in 2018. Seeds of each variety were direct seeded at a ½” depth with a plate type push planter to achieve 12 seeds per foot. The spring trial was planted on April 23 and the fall trial was planted on August 10. The soil was a Hammonton loamy sand. In the spring trial Plots were 2 rows, 15’ long with 30” between rows. In the fall trial plots were 1 row 40’ long with 30” between rows. Narrow rows were not used due to the need to mechanically cultivate with available equipment. The experimental design was a randomized complete block with 6 replications in the spring and 4 replications in the fall. Herbicides applied were: Ro-Neet 2 qt./a preplant incorporated and Spin-Aid 2 pints/a postemergence. Fertilizer applied preplant included 50 lbs. N and 140 lbs. K20 per acre with 3 lbs. of B. Additional N was applied at a rate of 50 lbs. N per acre 6 weeks after planting. Five weekly applications of Dipel insecticide were made from week 3 in each trial. Fungicide was applied two times and consisted of azoxystrobin (Quadris) plus copper. Irrigation was provided by overhead sprinklers (linear system). Plots were cultivated twice and were also hand weeded in the row.

Plots were harvested starting July 5 in the spring trial and November 19 in the fall trial. Taunus, Boldor, and Soldier were not harvested in the fall trial due to lack of size (did not reach harvest maturity). A 10’ section of row was harvested in both rows in the spring trial and a 20’ section of row was harvested in the fall trial. Beets were pulled by hand, tops removed and weighed and then roots counted and graded into small (1-2” diameter), medium (2-3” diameter) and large (>3” diameter) grades. Each grade was then weighed. Selected beets from each replication were cut, juice extracted, and then measured for soluble solids using a refractometer. Roots were also evaluated for uniformity of size (1-10 with 10 being all the same size), uniformity of shape (1-10 with 10 being all the same shape), exterior appearance (1-10 with 10 being excellent appearance) and interior color (1-10 with 10 being excellent color appropriate for the variety). Tops were evaluated for leaf disease in the spring planting (1-10 with 10 being disease free).

The spring planting received 2.5 inches of rainfall one day after planting and emergence was delayed and stand reduced due to surface compaction which reduced yields. Kestrel had the highest yield (15.2 tons/a). Other varieties with yields above 11 tons per acres were 3×5, 3×11, Red Ace, Red Kite, Bohan, Pablo, Avalanche (white), Red Cloud, Red Atlas, and Bresko. This group ranged from 11.1 to 13.8 tons/a. Low yielding varieties under 7 tons/a were Soldier (red leaf type) and Boldor (yellow root type). In the fall trial, stands were thicker than desired (not thinned) so roots were smaller; however, yields were good. Those varieties in the fall trial with yield greater or equal to 20 tons per acre included Falcon, Red Ace, 3×11, Red Atlas, Boro, 3×5, and Merlin (range from 22.3 to 20.0 tons per acre). Those varieties yielding under 20 tons/a were Bresko, Bohan, Manolo, Pablo, and Moneta (14.2, 14.0, 13.8, 12.7, and 12.6 tons/a respectively).

In the spring planted trial, Red Ace had the highest number of harvested beets per plot (42) followed by Kestrel (34), 3×11 (32), and 3×11 (31). The varieties 3×5, 3×11. Bohan, Boro, Falcon, and Red Atlas had over 2000 g/plot in the large size grade; 3×5, 3×11, Falcon, Kestrel, and Red Kite had over 2000 g/plot in the medium size grade, and 3×5, 3×11, and Kestrel had over 1700 g/plot in the small size grade. The most vigorous tops by weight were 3×5, 3×11, Bohan, Falcon, Kestrel, Red Kite, and Soldier (all over 2000 g/plot). In the fall trial, Red Atlas had the highest number of harvested beets per plot (94) followed by Red Ace (91), Red Titan (89), 3×11 (83), Merlin (83), Pablo (82) and Falcon (80). Falcon had the highest weight of large beets (1086 g/plot), Red Titan had the highest weight of medium beets (2050 g/plot), and Red Atlas had the highest weight of small beets (4245 g/plot). Falcon and Kestrel had the most vigorous tops by weight (6014 and 5030 g/plot respectively).

In the spring planted trial, Avalanche, Pablo, Red Ace, and Red Titan had the most uniform root sizes and shapes (above 5 rating for both). 3×5, 3×11, Red Atlas, and Red Cloud had the least foliar disease (rating above 6). Moneta had the best exterior root appearance (rating of 6.5) and Bresko, Moneta, and Pablo had a rating of over 8 for interior root appearance. Varieties in the spring trial with a brix % over 6 were Boro, Bresko, Falcon, Kestrel, Red Atlas, and Soldier. In the fall trial, 3×11, Moneta, and Red Titan had the most uniform root size and shape ratings (above 6). The varieties 3×5, Manolo, Red Ace, Red Atlas, and Red Titan had the best exterior root appearance (all above 6). Avalanche, Kestrel, Moneta, and Red Cloud had the best interior root appearance (all above 6). The varieties with the highest brix % were Merlin (7.2), Falcon (6.5), Manolo (6.5), Red Atlas (6.5), Kestrel (6.3) and Pablo (6.3).

These trials showed that beets could be successfully grown to commercial yields under Delaware conditions in both spring-planted for summer harvest and summer-planted for fall harvest.

Red Titan, Falcon, Soldier (Bulls Blood), Taunus (long), Boldor (yellow), and Avalanche (white) beets from left to right.

Red Ace, 3×11, Boro, and Red Atlas beets

Hot Water Treatment of Seeds

Gordon Johnson, Extension Vegetable & Fruit Specialist;

We have had an increase in bacterial diseases of vegetables that are seed transmitted such as black rot of cole crops.

Hot water treatment of seeds is a method to eliminate certain seed borne diseases of vegetable crops. This treatment has the benefit of killing pathogens that may be found on and within the seed coat.

From the Mid Atlantic Commercial Vegetable Production Recommendations:
“Seed heat-treatment follows a strict time and temperature protocol, and is best done with thermostatically controlled water baths. Two baths are required: one for pre-heating and a second for the effective pathogen killing temperature. The initial pre-heat treatment is 10 minutes at 100ºF (38ºC). The effective temperature treatment and time in the second bath differ between crops; protocols for several important crops are listed in Table E-10. Immediately after removal from the second bath, seeds should be rinsed with cool water to stop the heating process and dried on screen or paper. Seeds may be re-dusted with fungicide if desired. Pelleted seed is not recommended for heat treatment. Heat treat only seed that will be used during the current season. See crop sections for specific seed treatment recommendations.”

List of seeds that can be treated, treatment times and temperatures, and diseases controlled can be found at

The University of Delaware Extension Vegetable program has the equipment to hot water treat seeds. Please contact Gordon Johnson or Emmalea Ernest to arrange to hot water treat seeds.