Volume 26, Issue 13 June 22, 2018

Vegetable Crops Downy Mildew Resistant – Gordon Johnson, Extension Vegetable & Fruit Sweet Corn Insect Management – David Specialist; [email protected] Owens, Extension Entomologist, With downy mildew being found in pickling [email protected] and Bill Cissel, Extension cucumbers on Delmarva, resistant varieties Agent – Integrated Pest Management; should be considered. [email protected] We now have several slicing and pickling Sweet corn trapping data is updated by Tuesday cucumbers with some degree of resistance to the and Friday mornings and can be accessed here: current aggressive downy mildew http://agdev.anr.udel.edu/trap/trap.php . I strain. According to Clemson University new expect earworm counts to start decreasing; you research has identified two strains of cucurbit can look at our historical trapping data downy mildew: A1 attacks cucumber and Trap BLT – CEW Pheromone Corn cantaloupes (the most aggressive strain), while Location (3 nights CEW Spray A2 attacks watermelon, pumpkins, and squashes. total (3 nights Schedule In gynoecious slicing cucumbers, Bristol, catch) total catch) SV3462CS and SV4719CS and associated Dover 1 8 4 day pollenizers have intermediate resistance to Harrington 0 4 4-5 day cucumber downy mildew. In gynoecious pickles, Milford 0 3 5 day Citadel, Peacemaker, and SVCN6404 with Rising Sun 0 22 4 day associated pollenizers have intermediate Wyoming 0 0 No spray resistance. Next generation downy mildew Bridgeville 0 12 4 day resistant varieties are being tested this year on Concord 0 3 5 day Delmarva. Georgetown 0 0 No spray These varieties are not immune to downy Greenwood 0 0 No spray mildew, but they show less disease under the Laurel 0 7 4 day same pressure and will out yield susceptible Seaford 0 0 No spray varieties. Under disease pressure they perform The spray schedule listed in the table is based best with a fungicide program using downy off our sweet corn action thresholds which can mildew materials. Research is being conducted be found here: to see if there is the potential to reduce http://extension.udel.edu/ag/insect- fungicide applications. management/insect-trapping-program/action- thresholds-for-silk-stage-sweet-corn/ . Shown in the table below is the yield of pickling cucumber varieties with and without intermediate resistance to cucumber downy

June 22, 2018 Weekly Crop Update Volume 26, Issue 13 1 mildew with one fungicide application for downy Lack of fruit set can result from a lack of mildew under moderate disease pressure. Note due to reduced activity, reduced that the resistant varieties significantly viability, or reduced pollen germination in outperformed the susceptible variety high heat. As an example, a female watermelon (Georgetown, DE, 2017). will need around 500-1000 pollen grains to be fertilized effectively. This will require a Variety Yield minimum of 8 visits by a honey bee. Research Bu/a has shown that over 20 visits may be required to SVCN6404 + SV2987CL pollenizer 329 a achieve full set and full size in some cucurbits. (Resistant) Citadel + SV2987CL pollenizer 276 b This year (2018), early fruit set in watermelon (Resistant) and cantaloupe may be off due to poor weather Vlaspik + Sire pollenizer 214 c during early flowering. flights are reduced (Susceptible) significantly in rain and when winds are 15 mph p 0.001 or greater. Cloudy weather also reduces bee activity. Bees also do not fly much below 55°F, so on cold mornings, as we often had in June, bee activity will not pick up until later in the morning. Unfortunately, female watermelon open early in the morning, are most receptive before 10 am, and then close in the afternoon. In addition, in early mornings and during poor weather, bees usually visit closest to the hives. As the temperature rises or the weather improves, the bees will forage further from the hive. This means that in bad weather vine crops closest to the hives will have the best set and furthest from the hives will have the worst. This year another problem is that some watermelon fields have lost significant numbers of pollenizer plants due to poor weather conditions during or after planting. This means Downy mildew pressure with susceptible and that pollen will be limiting. Research has shown resistant varieties planted side by side in a trial that were pollen is limiting, fruit numbers will located on the Eastern Shore of Maryland in be reduced with distance from a pollen source. 2018. In fields with limited pollen, expect reduced fruit set or reduced fruit size in areas where pollenizers are missing. Fruit Set and Fruit Carry in Cucurbit Vine Another common question from growers and Crops – Gordon Johnson, Extension Vegetable & crop consultants is how many fruit should a Fruit Specialist; [email protected] carry and what will affect fruit “carry” in vine Watermelons and cantaloupes are setting fruit, crops. pickle harvest is underway, summer squash is in For watermelons, a healthy, vigorous plant may full production and pumpkin planting is finishing set 3-7 fruits initially. However, for mid-size and up. With the many rainy days as well as high larger watermelons, the plant will only carry 2-4 winds and storm damage this season, fruit loads fruit at any time. Smaller fruited varieties will in some early planted vine crops has been more fruits per plant but essentially the same affected and higher numbers of quality defects total pounds as larger types. This is the carrying are evident. capacity of the plant and is directly related to

June 22, 2018 Weekly Crop Update Volume 26, Issue 13 2 the quantity of photosynthates being produced harvested as are watermelons. Medium sized by the plant, mostly in the leaves. Any Jack-o-lantern types will carry 1-2 fruits, larger additional fruits, even if initially set, will be types closer to 1. All others will be aborted. aborted. Once the first fruit ripens and is Smaller types will carry more depending upon harvested, additional sets can be carried. To their size in pounds (for example a variety with 5 carry the maximum amount of fruit, it is lb average will carry 4-7 fruits). Maximum necessary to maintain high plant vigor and good carrying capacity in pumpkins is largely affected foliage health. This requires paying close by variety (varieties with some heat tolerance attention to irrigation and fertility programs; will carry more fruits in our climate) and foliage having excellent disease, insect, and mite health. Excess nitrogen fertilization will often control; and having good activity delay fruit set in pumpkins. during pollination and fruit set. In watermelons, if average fruit carry is less than 2 per plant, this In gynoecious cucumbers grown for once over is a sign that the plants have reduced vigor and pickle harvesting, there will be two fruits set on are under stress. Repeated fruit set depends on adjacent nodes that are ready for harvest at any maintaining vine health through the season. one time. These will be set on nodes 2-6 commonly. The pollinizers that make up a small Another factor to consider is where fruit set is percentage of the population will set pickles occurring. Crown sets are desired in every fifth node generally and therefore only watermelons, especially in early plantings. one fruit will be ready for harvest. Yield Crown sets are those that occur on nodes closest reductions in gynoecious pickling cucumbers to the base of the plant, within the first 8 nodes. occur when there is a loss of set so that fruits Having good crown sets requires that plants have are not on adjacent nodes. Parthenocarpic good early growth so that adequate leaf area is pickle varieties that set fruit without pollination produced that can support early set fruit as well will commonly have 3-5 pickles on adjacent as proper pollination (sufficient bees). Lack of nodes ready for harvest at any one time. This crown set is a sign of poor early growth, early allows them to be planted at much lower plant stress, or of problems with pollination. densities.

Growers with early-planted watermelons this year (those planted the last week in April or first 2 weeks in May) are likely to see reduced crown Tomato Pith Necrosis – Jerry Brust, IPM set and may see increased numbers of seedless Vegetable Specialist, University of Maryland; melons with defects such as distinct lobes [email protected] (noticeably triangular) or hollow heart and standard seeded pollenizers with pinched ends. In the last week, tomatoes from different These are signs that pollination was lacking counties in Maryland were found with the same during early fruit set. This can occur when there unusual disease symptoms, called tomato pith is a lack of pollen – pollenizers have not necrosis. All the problem tomatoes were from produced enough male flowers or are delayed in early planted fields. Tomato pith necrosis is producing male flowers. In some years, fields caused by the soilborne bacterium Pseudomonas have had losses of pollenizers, due to the poor corrugata. It has occurred infrequently in weather during transplanting, requiring Maryland over the past few decades. The disease replanting. This may reduce pollen for the first usually is found in early planted tomatoes when set female flowers in triploids, reducing crown night temperatures are cool, but the humidity is sets. Reduction in bee activity during the stormy high, and plants are growing too rapidly because weather this June may also reduce early sets. of excessive nitrogen application. We have had a Early plant stress such as the wind damage, spring with some cool nights in May and high flooding, and hail damage we have seen this humidity with all the rain we had. In the field, year can also cause abortion of flowers leading diseased plants occur randomly with initial to reduced crown set. symptoms often seen as the first fruit clusters reach the mature green stage. Symptoms include With pumpkins, harvest is limited to those fruits chlorosis (yellowing) of lower, middle and even set initially, because pumpkins are not repeat younger leaves (Fig. 1) followed by wilting of the

June 22, 2018 Weekly Crop Update Volume 26, Issue 13 3 infected shoots in the upper part of the plant canopy. This wilting is usually associated with internal necrosis at the base of the stem and black streaking may be apparent on the surface of the main stem, which often splits (Fig. 2). When the stem is cut open along its length or cross-wise (Fig. 3) the pith will be discolored and may have hollow areas. There is often prolific growth of adventitious roots in the stems with discolored pith, and the stems may appear swollen (Fig. 4). Figure 3. Darkened pith of tomato stem There is little that can be done for control of pith necrosis. The best practice is prevention by avoiding the use of excessive amounts of nitrogen in tomato, especially early in the season when nights are still cool. There is some evidence that the pathogen may be seedborne, but more research is needed on the epidemiology and management of this disease.

Figure 4. Prolific growth of adventitious roots on stem

Figure 1. Beginning of pith necrosis- leaves turn Watch for Thrips in Vegetables – Jerry Brust, yellow IPM Vegetable Specialist, University of Maryland; [email protected]

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- Figure 2. Tomato stem with dark streak and orange insects the size of metal filings with lesions on its surface fringed wings. They feed by puncturing the outer layer of plant tissue and sucking out the cell contents, which results in stippling, discolored

June 22, 2018 Weekly Crop Update Volume 26, Issue 13 4 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 Figure 1. Early thrips feeding on tomato leaf, plant-feeding species lay their kidney-shaped black specks are thrips feces (A) and later eggs on or into plant tissue. The prepupae and feeding damage (B) 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 Figure 2. Pepper leaf distortions due to thrips extent. Thresholds for vegetables are: flowers of feeding 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 SNAP Electronic Benefit Transfer (EBT) fruit quality. One or two applications of a Equipment Options for Farmers’ Markets – pyrethroid or neonic or spinosad (see 2018 Mid- Nancy Mears, Extension Agent - Family and Atlantic Commercial Vegetable Production Consumer Science; [email protected] Recommendation Guide) applied with enough water (80-100 gal/a) should control most thrips Did you know that Approximately $17.6 million infestations. Spraying more than 4-5 times for of SNAP Benefits issued each month in Delaware? thrips in a 4-5-week period will usually lead to The USDA Food and Nutrition Service places a an even worse thrips problem. This is because high priority on expanding SNAP participants’ the sprays will reduce eastern flower thrips and access to fresh and healthy food through farmers other thrips species, but usually not western markets and direct marketing farmers, flower thrips that are often resistant to many encouraging participants to spend their benefits insecticides. Once the thrips population consists on healthy foods. mostly or entirely of western flower thrips it may not be possible to get the population under FNS’ EBT Equipment Program offers low-cost, reasonable control. wireless EBT point-of-sale (POS) equipment to eligible markets and farmers. The program pays for the equipment and service fees for up to 3 years, including set-up costs, monthly statement fees, and wireless plan fees. The market or

June 22, 2018 Weekly Crop Update Volume 26, Issue 13 5 farmer is responsible for paying transaction Growing Degree Days (GDD) and Rainfall costs, the costs of scrip systems (paper, ink, Through June 19 - Jarrod O. Miller, Extension tokens, etc.), and fees to terminate an existing Agronomist, [email protected] contract. The program will be available very soon to eligible farmers and farmers’ markets. With dry weather the last week we have finally To be contacted when the program resumes seen steady field work and replanting going on. operations, please email If you look at the graph of statewide [email protected]. accumulation, the last week has been the longest period without rain for most of the state this planting season. Ground has dried out fast, Fruit Crops or it may appear that way once we got used to constant saturation. So be sure to check your soil Spotted Wing Drosophila Management moisture and irrigate if you need to. With Strategies – David Owens, Extension minimal root development under saturation, Entomologist, [email protected] field crops may not reach soil moisture even if it is just six inches down. If you have to contend with spotted wing drosophila, the following Extension publication As long as it wasn’t drowned out, any corn may be a useful resource for combining multiple planted between April 22 and June 3 should have strategies to lessen damage and prevalence, had plenty of GDD to emerge. Here are some especially for organic production systems: general guidelines to GDD to monitor your corn https://secure.caes.uga.edu/extension/publicat fields and see if they are growing normally. ions/files/pdf/B%201497_3.PDF. V6: 475 GDD V12: 870 GDD VT: 1135 GDD Agronomic Crops R1: 1400 GDD

Soybean Insect Scouting Update – David Table 1: Growing degree days accumulated Owens, Extension Entomologist, through June 19th from the beginning of each [email protected] and Bill Cissel, Extension week. Agent – Integrated Pest Management; [email protected] Low populations of bean leaf beetles, grasshoppers, green cloverworm, bean leaf rollers and soybean leafminer, and thrips are being observed in soybeans. We are also seeing spider mite hotspots in a couple of the oldest fields. Levels are not yet of concern, but with warm temperatures, keep an eye on their populations. Interestingly, we have been seeing thrips hotspots in Kent County. In the experience of other university entomologists, 95% of the time, thrips do not cause yield reductions. There is a general guideline where if most of the leaves are injured, and there are more than 8 thrips per leaflet and the field is stressed, they can be significant. That is, are the plants being ‘held back’? Are they not growing? Soybean that is growing can tolerate a great deal of feeding.

June 22, 2018 Weekly Crop Update Volume 26, Issue 13 6 mite numbers, but many fungicides slow down or General prevent fungal growth.

Managing Spider Mites in Soybeans and Action thresholds for watermelon are 20 – 30% infested plants with 1 – 2 mites per leaf. For R- Vegetables – David Owens, Extension stage soybean, thresholds are 20-30 mites per Entomologist, [email protected] and Bill Cissel, leaflet and 10% of plants with one third of the Extension Agent – Integrated Pest Management; leaf area stippled. For tomato, NCSU [email protected] entomologist Dr. James Walgenbach We found our first two spotted spider mites in recommends an action threshold of 2-4 mites per watermelon, cantaloupe, and soybean last week. leaflet. On tomato, spider mites can also be a Spider mites move into fields in 3 ways: hitching contributing cause of ‘gold-fleck.’ a ride on equipment or workers, crawling over NCSU research indicates that two spotted spider soil, or by being transported by wind. When host mite resistance is unstable. If mites are resistant quality declines, TSSM will move to high objects at the end of one season, that resistance will not and stand on their ‘tip toes’, waving their first be as strong at the beginning of the next. pairs of legs until a passing air current catches However, resistance is still present and can be them. rapidly selected for. There is limited population Spider mites quickly reproduce with the warm mixing from one farm operation to another. weather that we have had. Mites can develop What this means is that a population of mites on from egg to adult in as few as 8 days, and lay one farm does not spread to others. This means over 140 eggs during their 2 to 3-week life span. that miticide rotation is extremely important. Eggs take about 6 days to hatch. Even with the Miticides tend to be most active on certain wet weather we have had, it is possible that demographic groups, meaning that there is likely spider mites may need treating at some point in a subset that will not be killed from the your fields later this season. Humid weather application. Given their life span (6 days as eggs, favors entomopathogenic fungi which can reduce 8 as juveniles), if you need to spray, anticipate a second application. The table below lists the miticide active ingredients and their mode of action group for watermelon. There are generic formulations of some of the chemicals, this list is not meant to serve as an endorsement. Miticide Active MOA group Life stage active Applications/season ingredient Agri-Mek Abamectin 6 Mobiles (translaminar) 3-5 Gladiator Zeta- 3 + 6 Mobiles (translaminar) 3 cypermethrin + avermectin Acramite Bifenazate 25 Mobiles, some ovicidal 1 (contact) Kanemite Acequinocyl 20B Mobiles, some ovicidal 2 (translaminar) Oberon Spiromesifen 23 Eggs and juveniles 3 (contact) Portal Fenpyroximate 21A Mobiles (contact) 2 Zeal Etoxazole 10B Ovicidal, juveniles 1 (translaminar)

Please note that avermectin is in the same mode products will stop mite feeding quickly, but the of action class as abamectin. Do not apply one mite will take a few days to die. If you have right after the other. Also, some of these sprayed a field and see mites a couple of days

June 22, 2018 Weekly Crop Update Volume 26, Issue 13 7 later, wait another few days and resample. Also, There are many different species of Carabidae many of these products have a long residual beetles, commonly referred to as ground activity, meaning that if it is not active beetles, which can be found in crop fields that immediately on eggs, it should still be around are helping to keep pest populations in check. once the eggs hatch. This year, we have plans to However, they aren’t all as attractive as this test these products at our research station. particular species of ground beetle. Ground beetles are considered “generalist predators” For soybean, three materials have been meaning they prey on many different kinds of previously recommended: bifenthrin (a pests. One pest that they are known to prey on pyrethroid), Agri-Mek 0.7SC, and Zeal 2.88SC. is slugs. With very few natural enemies, gaining Generally speaking, pyrethroid resistance can be a better understanding of the predator-prey an issue with spider mites. This class will also relationship between ground beetles and slugs remove beneficial predatory insects. can provide valuable insight into how we can As always, read the label thoroughly for further take advantage of these natural enemies to help guidance. Some products have restrictions on with slug control. reapplication interval, and restrictions on Curious about some of the current Delaware consecutive applications. There are also Soybean Board funded research being conducted requirements on some for spray adjuvants to at the University of Delaware? avoid illegal residues. Good coverage is key for miticide efficacy, even on those that are Click on the link to watch a short (90 second) translaminar. Youtube video to learn more about some of our research with ground beetles and slugs:

https://youtu.be/fSMX74XhSbI Guess the Pest! Week #12 Answer: Ground Fun Entomology Fact: In Europe, there is a Beetle - Bill Cissel, Extension Agent – species of ground beetle that is commonly Integrated Pest Management; [email protected] referred to as the “Slug Killer”.

Congratulations to Chris Williams for correctly identifying the insect in the photo as a ground beetle and for being selected to be entered into Guess the Pest! Week #13 – Bill Cissel, the end of season raffle for $100 not once but Extension Agent – Integrated Pest Management; five times. Everyone else who guessed correctly [email protected] will also have their name entered into the raffle. Click on the Guess the Pest logo to participate in Test your pest management knowledge by this week’s Guess the Pest challenge! clicking on the GUESS THE PEST logo and submitting your best guess. For the 2018 season, Guess the Pest Week #12 Answer: Ground we will have an “end of season” raffle for a Beetle $100.00 gift card. Each week, one lucky winner will also be selected for a prize and have their name entered not once but five times into the end of season raffle.

This week, one lucky participant will also win A Farmer’s Guide To Corn Diseases ($29.95 value).

June 22, 2018 Weekly Crop Update Volume 26, Issue 13 8 You can’t win if you don’t play! • Poultry Information • Diagnostic Information • Bee / Pollen Research • Wagon Tours Lunch will be provided REGISTER AT: https://2018-farmers-field-day-at- lesrec.eventbrite.com More Information to Follow. Check out Events at https://extension.umd.edu/lesrec The University of Maryland is an Equal Opportunity Employer and Equal Access Programs

Blueberry Experimental Plot Tour

Tuesday, June 26, 2018 6:00-8:00 p.m. What is the damage on the potato leaves? University of Delaware Carvel Research & Education Center 16483 County Seat Highway Georgetown, DE 19947 This meeting will highlight variety testing and other research with blueberries.

This is the last season that we will be maintaining and collecting data from the blueberry experimental Announcements planting at the research farm. Come see and taste the 25 varieties in the variety trial! 2018 Delaware Cooperative Extension Horticulture Short Courses Tour the blueberry variety trial, fertilization and soil amendment experiments. Register for this course online. The meeting will conclude with an ice cream and berry treat. 2018 Farmers’ Field Day At LESREC Wednesday, June 27, 2018 9:00 a.m.-1:00 p.m. Please pre-register by June 25 by contacting Karen University of Maryland Adams at (302) 856-7303 or [email protected]. Lower Eastern Shore Research & Education Center (LESREC)

27664 Nanticoke Road, Salisbury, MD 21801 Food Safety in Relation to Specialty Crops Calling all Farmers/Growers to Your Field Day at and Field Day LESREC Get the most out of your high value crops Topics • IR-4 Program Friday, July 6, 2018 8:30 a.m.-1:30 p.m. • Nutrient Management & Soil Health DSU Outreach & Research Center • Ag Law and Conserve (Possible Nutrient Mgmt. 884 Smyrna-Leipsic Road Smyrna, Delaware Credits) Focus is on cage culture, blueberry; EQIP program and • Plant Pathology Information organic farming; farmer perspective. • Variety Studies • Weed Management

June 22, 2018 Weekly Crop Update Volume 26, Issue 13 9 Dr. Rohan Tikekar of the University of Maryland will speak on food safety measures to use while working Weather Summary with fruits and vegetables on farm. Carvel Research and Education Center Georgetown, DE Week of June 14 to June 20, 2018 Dr. Gary Pavlis of Rutgers University will speak on production and management of a blueberry farm. Readings Taken from Midnight to Midnight

Participants will tour the farm! Rainfall: No rainfall recorded Please register by June 25, 2018 for this free field day/workshop by contacting Lekha Paudel at 302-857- 7796 or [email protected]. Air Temperature: Highs ranged from 91°F on June 18 and June 19 to 80°F on June 15.

Lows ranged from 76°F on June 19 to 56°F on June 16

Soil Temperature: 72.6°F average Additional Delaware weather data is available at http://www.deos.udel.edu/monthly_retrieval.html and http://www.rec.udel.edu/TopLevel/Weather.htm Weekly Crop Update is compiled and edited by Emmalea Ernest, Associate Scientist – Vegetable Crops University of Delaware Cooperative Extension in accordance with Federal civil rights law and U.S. Department of Agriculture (USDA) civil rights

regulations and policies, the USDA, its Agencies, offices, and employees, and institutions participating in or administering USDA programs are prohibited from discriminating based on race, color, national origin, religion, sex, gender identity (including gender expression), sexual orientation, disability, age, marital status, family/parental status, income derived from a public assistance program, political beliefs, or reprisal or retaliation for prior civil rights activity, in any program or activity conducted or funded by USDA (not all bases apply to all programs). Remedies and complaint filing deadlines vary by program or incident.

Reference to commercial products or trade names does not imply endorsement by University of Delaware Cooperative Extension or bias against those not mentioned.

June 22, 2018 Weekly Crop Update Volume 26, Issue 13 10