Broad Mites on High Tunnel Tomatoes

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

It is unusual that I see or hear about broad mites (Polyphagotarsonemus latus) being a problem in our tomato high tunnels. A grower was having symptoms of twisted growth and browning/bronzing of their tomato leaves this spring and guessed they might have broad mites. They did, with some plants severely damaged while others were fine. The grower had a late fall crop of cherry tomatoes that they kept into December but did not clean up until 2 weeks before they planted their spring crop of tomatoes. Unfortunately, the grower had a small infestation of broad mites in the fall crop of tomatoes that was able to overwinter. I wrote an article earlier this season about the necessity of cleaning a high tunnel or greenhouse well in advance of another crop in case there was a small infestation that had started in the last crop or on weeds left in the high tunnel. Sanitation is key to keeping pest problems out of a high tunnel or greenhouse.

Broad Mite Description and Biology
Female mites are oval, 0.2 mm long and are yellow or green with a light, median stripe that forks near the back end of the body. Males are similar in color but lack the stripe. The translucent, colorless oval eggs are firmly attached to the surface of a leaf. The eggs are very distinctive and are usually used to identify whether or not broad mites are present. (Often times adults or immatures cannot be found on a sample, but the eggs will be.) The eggs are covered with scattered white tufts on their outer surface that look like round dots (Fig. 1). Immature broad mites are white and slow moving. After just one day, the larva becomes a quiescent nymph which is clear and pointed at both ends. When females emerge from this quiescent stage, males immediately mate with them. Adult females lay a total of 30 to 76 eggs on the undersides of leaves and in the depressions of small fruit over a 9-14-day period and then die. Adult males may live 5-10 days. While unmated females lay eggs that become males, mated females usually lay four female eggs for every male egg. Males and females are very active, but the males account for much of the dispersal of a broad mite population when they carry the quiescent female to new leaves.

Figure 1. Broad mite egg greatly magnified

Hosts
The broad mite has a wide range of host plants: apple, avocado, cantaloupe, castor, chili, citrus, coffee, cotton, eggplant, grapes, guava, jute, mango, papaya, passion fruit, pear, potato, sesame, string or pole beans, tea, tomato and watermelon. Broad mites also infest many ornamentals, including African violet, ageratum, azalea, begonia, chrysanthemum, cyclamen, dahlia, gerbera, gloxinia, ivy, jasmine, impatiens, lantana, marigold, peperomia, pittosporum, snapdragon, verbena, and zinnia. Their ability to attack both vegetables and ornamental plants make them especially troublesome in greenhouses that grow both.

Damage
The damage caused by broad mites can look similar to the damage caused by viruses, herbicides or nutrient deficiencies. They feed on plant cells within the leaf epidermis using their piercing-sucking mouthparts. Early feeding is mainly concentrated near the growing point on the underside of a leaf near the stalk, which tends to cause the leaf to curl and become twisted and distorted (Fig. 2). More serious infestations cause leaf bronzing leaving the main veins green against the brown leaf tissue that eventually turns black, shrivels and dies (Fig. 3). Corky patches frequently appear on fruits that often crack at the site of deformation (Fig. 4). Extensive damage can be caused by relatively low populations. Commonly, the lower leaves of a plant can remain unaffected while the younger leaves are badly damaged. Symptoms of feeding damage can remain visible several weeks after the mites have been removed. Therefore, after treatments the plants need to be checked again for the presence of the mite, even though damage may still be apparent.

Figure 2. Leaves of tomato twisted and deformed by broad mite feeding

Figure 3. Broad mite feeding causing bronzing of leaves–leaving green veins

Figure 4. Damaged and aborted cherry tomato fruit due to broad mite feeding

Management
Once the mites have been positively identified as the cause of the tomato deformities horticultural oils or sulfur can be used that produce results similar to synthetic chemical applications. The most important aspect of the application is thorough coverage. The material needs to get down into tightly wrapped growing points and to the underside of leaves. Be careful when applying the oils or sulfur as they can cause phytotoxic problems under hot humid conditions. Portal XLO has been found to control broad mites in tomato and is classified as a mitochondrial electron transport inhibitor (METI) (IRAC subgroup 21A) and should be rotated with other miticides (hort oils, sulfur, Oberon, Agri-Mek) that have a different mode of action (i.e., a different IRAC No.). As in the case of oils and sulfur, Portal is a contact miticide and for best performance uniform and thorough spray coverage is needed. The addition of a nonionic wetting or penetrating adjuvant to the synthetic chemicals is recommended to improve their performance.

The Return of Red Legged Winter Mites

Jerry Brust, IPM Vegetable Specialist, University of Marylandjbrust@umd.edu

This past April I wrote an article about red legged winter mites, Penthaleus dorsalis, being found in a high tunnel on the eastern shore. I thought this was an odd, one-time thing. I have come to learn that the mites are unfortunately back in the grower’s heated high tunnel and more surprisingly have found that the same mites are causing all kinds of problems in high tunnels along the New England coast. This mite species is far more common than I had guessed and anyone now growing winter greens, crucifers, spinach and maybe leaf lettuces in high tunnels should be on the look out for this mite. Once it gets established in your high tunnel it is very difficult to manage.

 

Fall and Winter Crops are Just Getting Started in High Tunnels

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

As summer crops finish in high tunnels, October and November provides the opportunity to plant a wide range of vegetables for late fall and winter harvest. This is a way to continue providing fresh produce to CSA’s, farmer’s markets, restaurants, schools, and local retail.

Leaf Crops
Options for leafy greens from direct seeding include many mustard family crops such as kale, green and red mustards, arugula, Bok Choi, Napa cabbage, Asian greens such as mizuna, and turnip greens. Many of these greens will overwinter in a tunnel.

Many types of lettuce for cut salad greens and small heads can be direct seeded including leaf types, butterhead-bibb types, romaine, and crisp head types. Lettuce can be grown throughout the fall and winter months.

Beet family greens including beets for greens, swiss chard, and spinach direct seeded in October will provide long term harvests into mid-winter.

Other cool season greens to try as a fall planting in high tunnels include corn salad, cress, and Claytonia.

Newly planted arugula in a high tunnel

Root Crops
Beets, carrots, radishes, and turnips seeded in the high tunnel in October and early November will provide late fall and early winter harvests.

Alliums
Leeks transplanted now for overwintering will allow for late winter and early spring harvest. Green onions (scallions) will produce a fall crop from transplants and will overwinter from direct seeding to produce an early spring crop. Chives and garlic chives seeded in October will produce a crop from late fall through spring.

Other Possibilities
Thick seedings of peas (green shelled or field peas) will provide plentiful pea shoots throughout the late fall and winter.

Herbs such as parsley can be seeded now for late fall through early spring harvest. Cilantro is an excellent choice for fall high tunnel production from direct seeding. There are also several perennial herbs that will produce well from late fall through winter (thyme, oregano, sage, rosemary, mint as examples).

Extending Your Strawberry Season with Day Neutral Varieties

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

Plasticulture strawberry planting season is quickly approaching. Growers seeking to extend their strawberry seasons should consider planting a portion of their area to day-neutral varieties. Day-neutral strawberries start fruiting 12-14 weeks after planting and have the potential to give late fall as well as early April through July production. Currently, the three varieties that have shown the most potential for extended production on Delmarva are Seascape, San Andreas, and Albion.

Albion, in particular, has shown great flexibility for season extension. It is very flexible on when it is planted in the late summer or early fall. August plantings will yield some late fall production, particularly in high tunnels. While much less productive in the main Chandler season in the spring, it has some unique properties that make it valuable to growers. First, it will give some early production, ahead of Chandler. Second, even though production is lower, it produces evenly over an extended period of time from April through July. In general, it will give 5-6 weeks more production than Chandler. It is a large, firm berry that, while not as sweet early in the season, has good quality in May and June.

Early August plantings of San Andreas will yield more fall production than Albion and San Andreas has comparable yields to Chandler in the spring with continued production through June. Both Albion and San Andreas have good quality and are firm berries that will stand up to regional shipping.

Seascape has been around for a long time and was the first of the larger sized day-neutral berries to show commercial potential in our area; however, Seascape has a softer berry and does not ship well so is best adapted to U-pick and local sales. Some grower in the region have had luck growing Seascape with multiple spring plantings spaced about three weeks apart from March through June giving summer and fall sales. Both Albion and San Andreas can also be planted in the spring for extended summer sales. Production in the heat of July and August will decline or stop unless there is a cool summer.

Because these day-neutral varieties keep blooming throughout the season, it is critical to maintain fertility, particularly with nitrogen, potassium, and calcium through fertigation. Albion, in particular, has high nitrogen needs to produce well. Disease management is also critical because these varieties bloom for an extended season. Gray mold fungicide sprays must be applied regularly throughout the extended seasons.

Notes from the Annual Meeting of the American Society for Horticultural Sciences (ASHS)

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

Each year, the ASHS has an annual meeting bringing together scientists working with specialty crops (vegetables, fruits, ornamentals). This year the meeting is in Washington DC. The following are some notes from sessions I have attended over the last 2 days that have relevance to our Delmarva growers.

  • Sweet corn planted into selected biodegradable black plastic mulches were shown to provide equal weed control, production, and earliness to standard black polyethylene mulch and eliminate mulch disposal costs.
  • Pepper production under biodegradable plastic mulch was equivalent to standard black plastic mulch again eliminating the need for mulch disposal.
  • Low rate compost application in potato (1 ton/a) reduced nitrogen needs and improved quality and yield in potato production.
  • Reduced curing temperatures and time of curing as well as delayed vine termination (mowing just before digging) reduced internal defects in ‘Covington’ sweet potato
  • Using white or reflective mulch did not improve broccoli production compared to black plastic mulch (we have a similar study currently in Delaware)
  • Progress is being made in breeding beets for lower levels of geosmin, the compound that gives beets the earthy taste.
  • Grafting tomatoes onto certain vigorous rootstocks can improve yield in high tunnel production, even in the absence of soil-borne disease.
  • From Matt Kleinhenz at Ohio State University “Commercial microbe-containing crop biostimulants are advertised to maintain or enhance crop growth. More than two-hundred such products ranging in composition (e.g., bacterial, fungal, both; cfu/ml) are currently available. To date, outcomes from standard statistical approaches common in product evaluations, variety trials, and cultural management comparisons show that significant increases in yield or quality have been rare, regardless of inoculation parameters or experimental conditions.”
  • A multistate project is underway to see if there are long term benefits to the “soil balancing” philosophy of soil management — specifically, balancing percentages and ratios of calcium, magnesium, and potassium through applications of lime, gypsum, and other materials to improve soil physics (tilth) and biology and, thereby, crop yield and quality and weed control. Past, shorter-term studies have shown no benefits to soil balancing but some growers and crop advisors disagree. This multi-state research aims at answering claims that University research on soil balancing has not been long term and thus is biased.
  • Recently, a finely ground (<0.5 micron) liquid limestone-based product (Top Flow 130; Omya, Oftringen, Switzerland) was developed for agriculture use to be injected through drip irrigation tubing. Research by Tim Coolong in Georgia showed that Top Flow 130 could be used to adjust pH in a plasticulture system, but that the effects would occur within a zone of 4 inches on each side of the drip irrigation tubing. This may be useful for situations where pH has dropped below 5.2 in plasticulture beds.
  • UV blocking plastic in high tunnel covers were shown to reduce Japanese beetle activity greatly in high tunnel raspberry production.

Problems with Pollination in High Tunnel Tomatoes

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

Some mid-Atlantic growers are seeing excessive tomato blossom drop in their high tunnels (HTs). Flowers are forming but then abscising from the plant (Fig. 1). In a few of the high tunnels bumblebees were used to pollinate the flowers (Fig. 2) and growers thought the bees were a little too aggressive in their pollination enthusiasm and that they were damaging the flowers (Fig. 3) to the point they would abort. But I think it is more likely environmental factors are causing the flower drop.

Figure 1. Flower abortion on tomato plant.

So, I’ll start with a quick recap as to how tomato flowers are pollinated and fertilized. Tomatoes are self-pollinated at the frequency of around 96% of the time. Tomato flowers are complete flowers that have both male (stamen) and female (pistil) parts within the same flower. The yellow anthers (pollen producing parts) of the stamen wrap around the pistil which is in the center of the flower. The style with the stigma on its end is the part of the pistil that extends above the anthers. Tomato pollen is heavy and sticky and needs to be jostled loose from the male to fall onto the female. This ‘jostling’ can include wind or insect visits. Once pollen is shed onto the stigma of the flower, fertilization can take place. Without pollination the pedicle turns yellow, the flower dies and then drops. Tomato flowers must be pollinated within 50 hours of forming or they will abort. Pollination usually occurs between 10 a.m. and 4 p.m.

Unfortunately, there are numerous factors that can cause tomato plants to drop their blooms. One of the main ones is temperature. Tomato plants will drop their flowers when daytime temperatures are above 85°F or when nighttime temperatures are above 70°F. Obviously this can and does occur during mid-summer. In the early part of the season low nighttime temperatures below 55°F can interfere with the growth of pollen tubes or cause the pollen to become sterile, preventing normal fertilization and causing flower drop. Fruit will not set until nighttime temperatures are above 55°F for at least two consecutive nights. The relative humidity (RH) also can play a role in poor pollination and fruit set. The best RH for tomato development is between 40% and 70%. Low RH (<40%) can dry pollen out making it unable to stick to the stigma. A high RH (>70%) can prevent the pollen from being shed properly. While there are other factors that have been found to influence pollination in tomato such as levels of nitrogen that are either too high or too low, too high or low soil moisture, a heavy fruit set, excessive wind that can desiccate flowers, and the lack of sufficient light these are minor factors compared with temperature.

Bumblebees pollinate tomato flowers by sonication or buzz pollination. They will fly up to a flower and grasp the anthers with their mouth parts and hold tightly. They then vibrate their wing muscles which causes pollen to drop from the anthers onto the stigma causing pollination and at the same time the bumblebee gets to collect some of the pollen (Fig. 2). This grasping of the tomato flower by the bee leaves a mark on the flower (Fig. 2) and can cause flower damage if visited too many times (Fig. 3). When there are fewer flowers than what would normally be expected fewer bumblebees should be released to prevent overzealous bee visits.

Figure 2. Bumblebee visiting tomato flower results in pollination. Arrow shows marks by other bee visitors.

Figure 3 These tomato flowers may have been visited too many times by bumblebees.

This year we have had an unusually cool spring and even in high tunnels the temperatures, especially at night, were not conducive for flower pollination and fertilization. Some growers who used bumblebees did have higher levels than usual of bee love as the bumblebees repeatedly visited the few flowers that were forming causing some of the flowers to abort. But this was a very small amount compared with what the cooler temperatures were doing to tomato pollination. Reports out of the Midwest and the Northeast say similar things, poor fruit set in high tunnel tomatoes up to this point in time and most of these high tunnels did not use bumblebees. Besides the direct effect of cooler temperatures on tomato pollination, the cooler than normal temperatures and often overcast skies also caused growers to not ventilate their HTs as much, reducing the probability of wind pollination of their tomato plants. Most growers depend on wind pollination for tomato pollination even in high tunnels. An excellent source for further description of problems with tomato pollination can be found at: Blossom Drop, Reduced Fruit Set, and Post-Pollination Disorders in Tomato by Monica Ozores-Hampton and Gene McAvoy, University of Florida HS1195: http://edis.ifas.ufl.edu/hs1195 .

Strange Mite Pest Found in High Tunnel Vegetables

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

Over the last three months a few early season high tunnel operations on the Eastern Shore were having problems with some of their seedlings and leaf crops. Crops like spinach would have ‘whitening’ and then browning and eventually dead margins of their leaves while seedlings would collapse. We found the problem to be ‘red legged winter mites’ Penthaleus dorsalis, which is a new pest in vegetables and herbs for us (Fig. 1). This mite was identified by Dr. Ron Ochoa, USDA, Beltsville. Because these mites are such new pests some of the information presented here is based on other closely related earth mite pest species.

Red legged winter mites thrive in what we would normally consider conditions too cold for an arthropod to cause problems. This mite is cold adjusted and cannot stand hot dry soil conditions and will die as summer heat approaches. Eggs are laid in late spring and they over-summer in the soil. These are stress resistant eggs (i.e., they can withstand drying and heat as well as synthetic chemical applications). In the fall they will begin to hatch, and mites will be active throughout the fall and winter inside a high tunnel with crops. Damage appears as ‘silvering’ or ‘whitening’ of the attacked foliage. Mites are most damaging to newly emerging crops, greatly reducing seedling survival and development.

Red legged winter mites are difficult to control even when using synthetic chemicals. Foliar sprays of Pyrethroids (check label for the particular crops that are labeled as this will vary greatly) or Pyrethrum + Neem or Beauveria bassiana + Pyrethrum will reduce feeding, but if mite populations are high it will be difficult to eliminate the damage. Applications should start as soon as damage is noticed before mites have a chance to build their population. Foliage should be thoroughly covered with spray material as should the base of plants.

Cultural controls involve using transplants instead of direct seeding, as the mites would do less damage to larger plants. Using high levels of heat such as clear plastic mulch to heat the soil and kill mites and, if used in the summer, kill even their eggs. Steam heat used to control nematodes and soil pathogens can be used to greatly reduce mite numbers before next fall’s planting. Many cultivations during the summer can significantly decrease the number of over-summering eggs that survive.

Figure 1. Penthaleus dorsalis

Growing Farmers Workshops

Coverdale Farm Preserve is a 356-acre farm and nature preserve located in Greenville, DE. We are pleased to offer a series of free hands-on workshops for farmers of all levels of experience and scale of operation. Registration is required. To register please contact Michele Wales: michele@delnature.org.

Spring 2017 Series: Protected Culture Growing includes the use of greenhouses, high tunnels, low tunnels, hoop houses, and caterpillar tunnels. Both high and low tech options are designed to help defend your crops against the extremes of nature from torrential rains, parching drought, scorching heat, and frigid cold. Protected Culture Growing extends your seasons, brings harvests earlier in spring and later in fall to your customers, and can be used on acres of open field to urban raised bed gardens. Engage in hands-on workshops that take you from construction to production targeting key topics for your growing success.

 

Troubleshooting in High Tunnels
Wednesday, June 21, 6:00pm – 8:00pm

Keep your plants thriving and productive. Learn to identify common pests including insects, plant diseases, nutrient deficiencies. Discover preventative strategies, steps, and solutions to compromising conditions in order to maximize yields.

Ethylene Problems in a Few Vegetable High Tunnels

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

Last week Gordon Johnson had an article about exhaust problems for greenhouse transplants. In Maryland we have seen a few problems with ethylene interactions with tomatoes in high tunnels. Ethylene (C2H4) occurs in trace amounts in gasoline and natural gas and is produced when these substances are burned. It is present in wood and tobacco smoke. Ethylene is also a plant hormone produced by plants during their growth and development. However, ethylene produced through defective heating equipment can be detrimental to protected crops, because the ethylene is produced in much greater quantities. Ethylene pollution influences the activities of plant hormones and growth regulators, which affect developing tissues and normal organ development, many times without causing leaf-tissue damage.

Injury to broad-leaf plants occurs as a downward curling of the leaves and shoots (epinasty); some growers think that this is wilting in the plant and look for root or irrigation problems that are not there. But a wilting plant is flaccid or soft and droopy with the leaves collapsed, while in epinasty the plant is turgid and firm, but with the leaves turned down (Fig. 1). How bad the down-turning of leaves is depends on the tomato variety, temperature, ethylene concentration, and the duration of exposure (see study by M. Jones at: http://u.osu.edu/greenhouse/2014/04/21/preventing-ethylene-related-losses-during-the-postproduction-care-and-handling-of-greenhouse-crops/). The epinasty then can be followed by stunting of growth.

Other symptoms of excess ethylene exposure include the abscission of flowers (Fig. 2), petals or leaves; water-soaking of older leaves; chlorosis; and wilting of flowers. Crops vary in their sensitivity and response to ethylene toxicity. High temperatures and high light levels will increase the severity of ethylene damage. In high tunnels that burn propane, kerosene or use motors that burn gasoline and have poor or no ventilation, even minute amounts of this pollutant can cause some damage to tomatoes. Symptoms of ethylene damage can be subtle, especially if there are no plants grown in non-polluted air for comparison. Often times the damaged tomatoes show up in unexpected areas of a high tunnel–sometimes in the middle of the high tunnel with a group of 5-10 plants affected and no tomato plants around them with any symptoms. This is due to the patterns of air movement in high tunnels that are passively vented and not as predictive as in actively vented situations. At times air patterns can concentrate the ethylene in certain areas one week and then in different areas the next week, making diagnoses of the problem difficult.

Proper heating system installation and maintenance are the best ways to prevent problems. Propane flames should have a small yellow tip when properly adjusted and natural gas flames should be a soft blue with a well-defined inner cone. To ensure proper combustion, heater units should have a clean air intake and should be vented to the outside with a stack, which keeps exhaust gas from being drawn back into the greenhouse through the ventilation system.


Figure 1. Tomato plants with a downward curling of leaves (epinasty) due to different levels of ethylene exposure.


Figure 2. Flower abortion on a tomato plant exposed to ethylene in a high tunnel.

Extending Your Strawberry Season with Day-Neutral Varieties

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

Plasticulture strawberry planting season is quickly approaching. Growers seeking to extend their strawberry seasons should consider planting a portion of their area to day-neutral varieties. Day-neutral strawberries start fruiting 12-14 weeks after planting and have the potential to give late fall as well as early April through July production. Currently, the three varieties that have shown the most potential for extended production on Delmarva are Seascape, San Andreas, and Albion.

Albion, in particular, has shown great flexibility for season extension. It is very flexible on when it is planted in the late summer or early fall. August plantings will yield some late fall production, particularly in high tunnels. While much less productive in the main Chandler season in the spring, it has some unique properties that make it valuable to growers. First, it will give some early production, ahead of Chandler. Second, even though production is lower, it produces evenly over an extended period of time from April through early July. In general it will give 5-6 weeks more production than Chandler. It is a large, firm berry that, while not as sweet early in the season, has good quality in May and June. Because plants are smaller and there are fewer berries per plant, it should be planted at a higher density than Chandler. Research has shown that planting three rows per plasticulture bed with two drip tapes provides the best yields.

Early August plantings of San Andreas will yield more fall production than Albion and San Andreas has comparable yields to Chandler in the spring with continued production through June. Both Albion and San Andreas have good quality and are firm berries that will stand up to regional shipping.

Seascape has been around for a long time and was the first of the larger sized day-neutral berries to show commercial potential in our area; however, Seascape has a softer berry and does not ship well so is best adapted to U-pick and local sales. Some grower in the region have had luck growing Seascape with multiple spring plantings spaced about three weeks apart from March through June giving summer and fall sales. Both Albion and San Andreas can also be planted in the spring for extended summer sales. Production in the heat of July and August will decline or stop unless there is a cool summer.

Because these day-neutral varieties keep blooming throughout the season, it is critical to maintain fertility, particularly with nitrogen, potassium, and calcium through fertigation. Over-fertilization with nitrogen will produce excess runners that will have to be removed and that will reduce productivity and under-fertilization with nitrogen will also limit production. Disease management is also critical because these varieties bloom for an extended season. Gray mold fungicide sprays must be applied regularly throughout the extended seasons.