Guess the Pest! Week #22 Answer: Helicoverpa zea, Corn Earworm

Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu

Congratulations to Amanda Heilman for correctly identifying the insect as an adult corn earworm and for being selected to be entered into the end of season raffle for $100 not once but five times. Everyone else who guessed correctly will also have their name entered into the raffle. Click on the Guess the Pest logo to participate in this week’s Guess the Pest challenge!

Guess the Pest Week #22 Answer: Helicoverpa zea, commonly known as corn earworm

The moth in the photograph is an adult Helicoverpa zea, commonly referred to as a corn earworm. The adult moth is a nectar feeder and not considered a pest. However, corn earworm larvae are considered by some to be the most economically important crop pest in North America. They are highly polyphagous meaning they feed on many different species of plants. Corn, especially sweet corn, is a preferred host plant. However, they also attack soybean, sorghum, snap bean, tomato, and cotton to name a few. Larvae prefer to feed on reproductive plant structures including blossoms, buds, and fruits. It is because of this large host range, and the fact that Helicoverpa zea larvae are so destructive that they are known by several other common names including tomato fruitworm, cotton bollworm, and podworm.

Tomato Problems

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

To no one’s surprise this week has seen a great number of problems pop-up in tomato fields throughout our area. The first, of course, has been disease with bacterial and fungal diseases spreading. The fungal pathogens usually can be contained with timely (as difficult as that is) fungicide applications. Bacterial spot or speck on the other hand can be much more difficult to control once it gets started and the weather remains wet and warm. In Figure 1 on the right hand side is a row of tomatoes that had been sprayed with fungicides and copper for the last several weeks. Bacterial spot has ravaged this row. The row to the left has been sprayed with the same material plus Actigard. Actigard is a plant activator that stimulates systemic acquired resistance, reducing the symptoms of bacterial and even fungal diseases. If you have problems with bacteria spot or speck Actigard can help reduce symptoms (as too can hot water treating your seed before you plant). You must use Actigard before the problem arises in the field, it is not a rescue material. This is the year in which the use of Actigard and heat-treating seeds would have greatly helped reduce losses to bacterial and fungal diseases.

Several fields had similar symptoms as seen in Figure 2, where the bottom foliage had been decimated but the top of the plant’s foliage looked good. If fungicide sprays are applied as needed the top foliage should be OK. The problem arises with the green fruit being exposed by the missing foliage. These fruits are in danger of sunburn, sunscald (Fig. 2) and rain check (the many, tiny concentric cracks that form on the shoulder of fruit and can expand over time (Fig. 3). This is where using shade cloth (20-30% shade-inducing) would greatly reduce the chances of sunscald and rain check. Gordon Johnson also had tips on preventing sunburn in vegetables in an earlier WCU article.

Figure 1. Row on right had fungicides and Cu applied, row on left same fungicides and Cu plus Actigard.

Figure 2. Bottom half of tomato plants have lost their foliage and expose fruit to possible sunscald or rain check

Figure 3. Exposed tomato fruit with rain check.

Odd Symptoms in Tomato Plants Turn Out to be Viruses

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

In Figure 1 you can see tomato plants that look a bit squirrely. I thought it was possibly herbicide or virus or nutrient problems. After eliminating the first and third we had the plants tested for a battery of viruses. There were 3 viruses found in the plants. The most unusual one was the Pepino mosaic virus, which belongs to the Potexviruses. This virus is very easily transmitted mechanically and has a low seed transmission rate. Seed transmission occurs at rates of less than one in a thousand when seed is not properly cleaned. The virus is external, contaminating the seed coat and not the embryo or endosperm. Symptoms very greatly with fruit marbling being the most typical and economically devastating symptom. You can also have fruit discoloration, open fruit, leaf blistering or bubbling, leaf chlorosis and yellow angular leaf spots. The severity of the Pepino mosaic virus symptoms is dependent on environmental conditions. As the infected plants mature the foliar symptoms usually disappear, but not the fruit problems. Prevention of infection is through stringent hygiene measures as the virus is spread primarily by mechanical methods.

The other two viruses found were more common: Tobacco (TMV) and tomato mosaic viruses. Tobacco mosaic virus is one of the most highly persistent tomato diseases because it can remain viable without a host for many years and it is able to withstand high temperatures. Both viruses are spread primarily by mechanical methods. Workers and their equipment can become contaminated when they touch infected plants. Symptoms are rather general and appear as yellow-green mottling on leaves with flowers and leaflets being curled, distorted, and smaller than normal in size. Generally, the fruit from TMV infected plants do not show mosaic symptoms but may be reduced in size and number and may develop an internal browning that most often appears in fruits of the first cluster. Severe strains of TMV and tomato mosaic virus can cause the lower leaves to turn downward at the petiole and become rough and crinkled. Some tomato varieties when infected with TMV or tomato mosaic virus can develop dead areas on leaves, stems and roots. As with the Pepino mosaic virus, the best control for these two viruses is strict hygiene and not using contaminated seed.

The Pepino mosaic virus is a newer one but is appearing more often in tomato production areas. The overall odd thing was that the symptoms on the plants did not fit any one of the viruses well. I attribute this to the mixture of viruses in the plant making it very difficult to observe characteristic symptoms of any one of them. Add to this that the environment plays a part in the plants expression of the symptoms as does the properties of the viral isolate and it becomes clearer why symptoms were not typical. The infected tomato plants were not commonly grown hybrid plants. Growers need to be sure about where their tomato seeds are coming from before using them.

Figure 1. Tomato plants infected with three different mosaic viruses

Mites Everywhere

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

There are reports of spider mites in multiple crops, with injury in tomatoes and a variety of cucurbits, mostly watermelon. Spider mites love hot, dry weather and that is what we have been having the last two weeks or so. They tend to start out at field edges or by drive rows. Anywhere dust settles on the crop is a likely spot for the earliest infestations. In watermelon, infestations usually start in the crown and spread from there. The oldest leaves will take on a yellow color along the midrib with necrotic spots (Fig. 1). This damage can be misjudged as a disease. Check for the mites on the underside of leaves to verify their presence (Fig. 2).

Figure 1. Mite damage to watermelon crown leaves

Figure 2. Two spotted spider mites on underside of watermelon leaf

For control there are several good miticides out there, but you need high gallonages of water 70-100 gallons/A and thorough coverage of the top and underside of the foliage or you will not reach all the well-hidden mites. Agri-Mek has translaminar movement, so if it is sprayed on the upper leaf surface it will penetrate into the leaf and reside there. Portal works on all stages of mites while Acramite is primarily active on the motile stages of mites (not eggs) and has a long residual. Oberon can take longer to work (check back in 5-7 days) but will give excellent control. Zeal is a growth regulator and will not kill adults but will kill immature mites, it works especially well if you catch the infestation early on. As always be sure to check the label before spraying any pesticides.

Blossom End Rot Revisited

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

Blossom end rot (BER) is showing up again this year in peppers and we expect it to be prevalent in tomatoes because of the recent hot weather. BER is a disorder where developing fruits do not have enough calcium for cell walls, cells do not form properly, and the fruit tissue at the blossom end collapses, turning dark in color. Calcium moves through cation exchange with water movement in the fruit, so the end of the fruit will be the last to accumulate calcium. Larger fruits and longer fruits are most susceptible. With fruits, the rapid cell division phase occurs early in the development of the fruit, the two weeks after pollination, and if calcium accumulation in the fruit is inadequate during this period, BER may occur. Over 90% of the calcium taken up by the fruit will occur by the time the fruit is the size of a nickel. While it may not be noticed until the fruit expands, the deficiency has already occurred and cells have already been negatively affected. We most commonly see signs of blossom end rot on fruits several weeks after the calcium deficiency has occurred.

Understanding blossom end rot also requires an understanding of how calcium moves from the soil into and through the plant. Calcium moves from the soil exchange sites into soil water and to plant roots by diffusion and mass flow. At plant roots, the calcium moves into the xylem (water conducting vessels), mostly from the area right behind root tips. In the xylem, calcium moves with the transpirational flow, the movement of water from roots, up the xylem, and out the leave through stomata. Calcium is taken up by the plant as a divalent cation, which means it has a charge of +2. It is attracted to negatively charged areas on the wall of the xylem, and for calcium to move, it must be exchanged off the xylem wall by other positively charged cations such as magnesium (Mg++), potassium (K+), ammonium (NH4+), or other calcium cations (Ca++). This cation exchange of calcium in the xylem requires continuous movement of water into and up through the plant. It also requires a continuous supply of calcium from the soil

In general, most soils have sufficient calcium to support proper plant growth. While proper liming will insure there is adequate calcium, it is not the lack of calcium in the soil that causes blossom end rot in most cases. It is the inadequate movement of calcium into plants that is the common culprit. Anything that impacts root activity or effectiveness will limit calcium uptake. This would include dry soils, saturated soils (low oxygen limits root function), compaction, root pathogens, or root insect damage. In hot weather on black plastic mulch, roots can also be affected by high bed temperatures. Low pH can also be a contributing factor. Calcium availability decreases as pH drops and below a pH of 5.2, free aluminum is released, directly interfering with calcium uptake. Again, proper liming will insure that this does not occur. Applying additional calcium as a soil amendment, above what is needed by normal liming, will not reduce blossom end rot.

In the plant, there is a “competition” for calcium by various plant parts that require calcium such as newly forming leaves and newly forming fruits. Those areas that transpire the most will receive more calcium. In general, fruits have much lower transpiration than leaves. In hot weather, transpiration increases through the leaves and fruits receive lower amounts of calcium. High humidity will reduce calcium movement into the fruit even more. Excess nitrogen that causes excess foliage will increase blossom end rot. Tissue tests will often show adequate levels of calcium in leaf samples; however, fruits may not be receiving adequate calcium. In addition, in hot weather, there is an increased risk of interruptions in water uptake, evidenced by plant wilting, when transpirational demand exceeds water uptake. When plants wilt, calcium uptake will be severely restricted. Therefore, excess heat and interruptions in the supply of water (inadequate irrigation and/or rainfall) will have a large impact on the potential for blossom end rot to occur. Proper irrigation is therefore critical to manage blossom end rot. This means a steady, even, uninterrupted supply of water in the soil surrounding the plant roots.

In high tunnels, lack of air movement can also be a factor, as transpiration is reduced, thus limiting calcium movement in the plant. In periods where tunnels are closed tight due to adverse weather, this may also increase the potential for blossom end rot. First fruits formed in early planted tomatoes and peppers are the most susceptible to blossom end rot, especially in high tunnels.

As a positive cation, there is “competition” for uptake of calcium with other positive cations. Therefore, if potassium, ammonium, or magnesium levels are too high in relation to calcium, they can reduce calcium uptake. To manage this, do not over-fertilize with potassium or magnesium and replace ammonium or urea sources of nitrogen with nitrate sources.

Applying additional soluble calcium through irrigation, especially drip systems, can reduce blossom end rot to some degree if applied prior to and through heat events and if irrigation is applied evenly in adequate amounts. Foliar applications are much less effective because fruits do not absorb much calcium, especially once a waxy layer has developed, and calcium will not move from leaves into the fruit (there is little or no phloem transport).

In conclusion, the keys to controlling blossom end rot are making sure roots are actively growing and root systems are not compromised, soil pH is in the proper range, and irrigation is supplied in an even manner so that calcium uptake is not interrupted. Supplemental calcium fertilization will only marginally reduce blossom end rot if water is not managed properly.

Sunburn in Fruiting Vegetables and Fruit Crops

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

Recent weather has produced conditions where there is high potential for sunburn in fruits and fruiting vegetables. Growers may need to consider ways to protect against sunburn. Sunburn is most prevalent on days with high temperatures, clear skies and high light radiation. We commonly see sunburn in watermelons, tomatoes, peppers, eggplants, cucumbers, apples, strawberries, and brambles (raspberries and blackberries).

There are three types of sunburn which may have effects on the fruits. The first, sunburn necrosis, is where skin, peel, or fruit tissue dies on the sun exposed side of the fruit. Cell membrane integrity is lost in this type of sunburn and cells start leaking their contents. The critical fruit tissue temperature for sunburn necrosis varies with type of fruit. Research has shown that the fruit skin temperature threshold for sunburn necrosis is 100 to 104°F for cucumbers; 105 to 108°F for peppers, and 125 to 127°F for apples. Fruits with sunburn necrosis are not marketable. Injury may be white to brown in color.

The second type of sunburn injury is sunburn browning. This sunburn does not cause tissue death but does cause loss of pigmentation resulting in a yellow, bronze, or brown spot on the sun exposed side of the fruit. Cells remain alive, cell membranes retain their integrity, cells do not leak, but pigments such as chlorophyll, carotenes, and xanthophylls are denatured or destroyed. This type of sunburn browning occurs at a temperature about 5°F lower than sunburn necrosis. Light is required for sunburn browning. Fruits may be marketable but will be a lower grade.

The third type of sunburn is photooxidative sunburn. This is where shaded fruit are suddenly exposed to sunlight as might occur with late pruning, after storms where leaf cover is suddenly lost, or when vines are turned in drive rows. In this type of sunburn, the fruits will become photobleached by the excess light because the fruit is not acclimatized to high light levels, and fruit tissue will die. This bleaching will occur at much lower fruit temperatures than the other types of sunburn. Damaged tissue is often white in color.

Storms that cause canopies in vine crops to be more open will expose fruits to a high risk of both sunburn necrosis and photooxidative sunburn.

Genetics also play a role in sunburn and some varieties are more susceptible to sunburn. Varieties with darker colored fruit, those with more open canopies, and those with more open fruit clusters have higher risk of sunburn.

Control of sunburn in fruits starts with developing good leaf cover in the canopy to shade the fruit. Fruits most susceptible to sunburn will be those that are most exposed, especially those that are not shaded in the afternoon. Anything that reduces canopy cover will increase sunburn, such as foliar diseases, wilting due to inadequate irrigation, and excessive or late pruning. Physiological leaf roll, common in some crops such as tomato, can also increase sunburn.

In crops with large percentages of exposed fruits at risk of sunburn, fruits can be protected by artificial shading using shade cloth (10-30% shade). However, this is not practical for large acreages.

For sunburn protection at a field scale, use of film spray-on materials can reduce or eliminate sunburn. These materials are kaolin clay based, calcium carbonate (lime) based, or talc based and leave a white particle film on the fruit (such as Surround, Screen Duo, Purshade and many others). There are also film products that protect fruits from sunburn but do not leave a white residue, such as Raynox. Apply these materials at the manufacturer’s rates for sunburn protection. They may have to be reapplied after heavy rains or multiple overhead irrigation events.

While particle films have gained use in tree fruits, their usefulness in vegetables is still unclear. Research in a number of states has shown reduced fruit disorders such as sunburn in peppers and white tissue in tomatoes when applied over those crops. Watermelon growers have used clay and lime based products for many years to reduce sunburn in that crop in southern states.

There are some drawbacks to the use of particle films. If used for sunburn protection on fruits, there is added cost to wash or brush the material off at harvest. Where overhead irrigation is used, or during rainy weather, the material can be partially washed off of plants, reducing effectiveness and requiring additional applications. Produce buyers can also have standards relating to the use or particle films and may not accept products with visible residues.

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.

Additional Labeled Uses for Torac in Vegetables

David Owens, Extension Entomologist, owensd@udel.edu

Several uses have recently been added for Tolfenpyrad, the active ingredient in Torac, a group 21A insecticide/group 39 fungicide. It has efficacy on thrips, aphids, several leps, and Colorado potato beetle. It is also labeled for powdery mildew. Torac is contact only. Crop sites and a few of the interesting pests that have been added are potatoes (potato beetle, leafhopper, aphids, thrips, psyllids), brassica leafy greens (aphids, flea beetles, thrips, maggots, diamond back moth), fruiting vegetables (aphids, thrips), and cucurbits (aphids, thrips, powdery mildew). The label also lists cucumber beetle as suppressive only. Supplemental labels can be found for the following

Aerial potato and potato: http://www.cdms.net/ldat/ldBMM011.pdf, http://www.cdms.net/ldat/ldBMM010.pdf

Fruiting vegetables: http://www.cdms.net/ldat/ldBMM006.pdf

Cucurbits: http://www.cdms.net/ldat/ldBMM005.pdf

Brassicas and brassica greens: http://www.cdms.net/ldat/ldBMM007.pdf, http://www.cdms.net/ldat/ldBMM012.pdf.

Please be aware that this product is toxic to bees, do not apply when bees are actively foraging. Please also refer to the specimen label for additional guidance: http://www.cdms.net/ldat/ldBMM000.pdf.

Watch for Thrips in Vegetables

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

I have gotten reports from flower growers of an inundation of thrips into their flower crop in the last week or so. I know, I know flowers are not vegetables, but many of the Flower thrips species that get into flowers will get into and on vegetables. Thrips are tiny, thin yellowish-orange insects the size of metal filings with fringed wings. They feed by puncturing the outer layer of plant tissue and sucking out the cell contents, which results in stippling, discolored flecking, or silvering of the leaf surface (Fig.1). Thrips feeding is usually accompanied by black flecks of frass (thrips poop) (Fig. 1). Pest thrips are plant feeders that discolor and scar leaf, flower, and fruit surfaces, and distort plant parts or vector plant pathogens. There are several species of vegetable thrips with the most common being the Eastern flower thrips, Frankliniella tritici, Tobacco thrips Frankliniella fusca, Western flower thrips, F. occidentalis and Onion thrips Thrips tabaci. The last three species are the ones most likely to transmit tomato spotted wilt virus, TSWV. Feeding results in various tissue responses, including scar formation and distorted growth (Fig. 2). Thrips hatch from an egg and develop into two larval stages and then the ‘prepupa and pupa’ stages, before becoming an adult. Females of most plant-feeding species lay their kidney-shaped eggs on or into plant tissue. The prepupae and pupae of most species drop to the soil or leaf litter to pupate. Thrips have several generations (up to eight) a year. When the weather is warm, the life cycle may be as short as 2 weeks.

It is difficult to identify thrips to species in the field. Thrips color, size, markings will not separate the different species found in our vegetable fields from one another to any great extent. Thresholds for vegetables are: flowers of tomato, pepper or watermelon can tolerate 5 thrips/flower with no fruit developmental problems. Squash and pumpkin flowers can tolerate 5-10 thrips/flower with no effect on fruit quality. One or two applications of a pyrethroid or neonic or spinosad (see 2018 Mid-Atlantic Commercial Vegetable Production Recommendation Guide) applied with enough water (80-100 gal/a) should control most thrips infestations. Spraying more than 4-5 times for thrips in a 4-5-week period will usually lead to an even worse thrips problem. This is because the sprays will reduce eastern flower thrips and other thrips species, but usually not western flower thrips that are often resistant to many insecticides. Once the thrips population consists mostly or entirely of western flower thrips it may not be possible to get the population under reasonable control.

Figure 1. Early thrips feeding on tomato leaf, black specks are thrips feces (A) and later feeding damage (B)

Figure 2. Pepper leaf distortions due to thrips feeding

Vegetable Disease Update – June 15, 2018

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

Tomato Late Blight
Tomato transplants were found at a garden center in northeast Pennsylvania last Friday (June 8) that were infected with late blight. We don’t know the origin of these transplants, and I understand that none were sold. However, the occurrence warrants extra vigilance of any tomato plantings to scout for late blight. Jerry Brust wrote a good article on recognizing the symptoms, which was published in last week’s WCU.

Cucurbit Powdery Mildew
Please read labels carefully as some of the fungicides mentioned in this article are not labelled on all cucurbits.

In planning your spray programs for powdery mildew on cucurbits, remember that many products that are labeled for this disease, are not effective because of the existence of fungicide resistance. The powdery mildew pathogen Podosphaera xanthii, is highly prone to the development of resistance and has lost sensitivity (become resistant) to some recently registered fungicides. To manage powdery mildew, begin with good cultural practices – especially the use of resistant cultivars. In a spray program, alternate targeted fungicides in different FRAC groups, apply fungicides at manufacturer’s recommended rate (don’t cut the rate), tank-mix with a fungicide with different mode-of-action (or use combination product), and don’t apply at-risk fungicides if powdery mildew sporulation covers more than 20% of the leaf surfaces.

Currently the following targeted fungicides are NOT effective for managing powdery mildew (resistance in pathogen population is high): Topsin M (FRAC 1, Benzimidazole), and Cabrio, Quadris, and others (FRAC 11, QoI fungicides).

Resistance exists, but the following fungicides may be used judiciously, to a limited extent, in a rotational program: Rally, Procure, Folicur, (FRAC 3, DMI fungicides); Pristine (FRAC 7 + 11), Fontelis, Xemium, Aprovia (FRAC 7, SDHI fungicides). Luna is also a FRAC 7 fungicide, however it isn’t cross resistant with the other FRAC 7 group.

Fungicides that still have good efficacy in our area in the past two years are: Quintec (FRAC 13) and Vivando (FRAC U8). Luna Experience and Quintec alternated with Procure are alternations that I have tested and performed well. Unfortunately, resistance to Torino (FRAC U6) has now been documented in the eastern U.S. and it hasn’t performed well in my trials.