Do you recognize stink bug injury on sweet corn?

As the brown marmorated stink bug (BMSB) becomes more well established around Ohio, its injury on sweet corn is becoming noticeable. In plantings that are sprayed frequently with pyrethroids such as Warrior or Hero for control of corn earworm, injury by stink bug is less likely to occur because pyrethroids are among the few insecticides that are toxic to stink bugs. But in plantings of transgenic sweet corn that do not need to be sprayed with insecticide for worm control, or in sweet corn that is sprayed by Coragen or Radiant for worm control, injury by stink bug is more likely to occur. Stink bugs feed by sucking juices from the kernels, after inserting their mouthparts through the husks (Figure 1). This results in kernels that are shrunken in a variety of ways, as shown in Figures 2 and 3 below. Both the adults (Figure 4) and the immature nymphs (Figure 5) feed on the kernels. The injury can occur anywhere on the ear; sometimes it is clustered near the tip, other times it is scattered along the entire length of the ear. In addition to sweet corn, BMSB has a wide range of host plants, ranging from raspberries, peaches, apples, and grapes to bell peppers, eggplant, green beans, swiss chard, and tomatoes.

-Celeste Welty, Extension Entomologist

Figure 1. Sweet corn ear being fed upon by adults and nymphs of the brown marmorated stink bug.

 

Figure 2. Sweet corn ear with many kernels injured by stink bug feeding.

 

Figure 3. Close-up view of kernels damaged by stink bug.

 

Figure 4. Adult of the brown marmorated stink bug.

 

Figure 5. Nymph of the brown marmorated stink bug.

Wayne County IPM Notes from August 16 – August 22

Vegetable Pests

Stink bugs have started to feed on and damage crops such as tomatoes. The stink bugs activity and feeding starts to increase most noticeably from late July through August and they remain active through the end of the growing season. Their damage on green tomatoes may appear as small, whitish areas. On ripe tomatoes, the damage shows up as a golden yellow “starburst” pattern. While this damage is typically only cosmetic, higher amounts of feeding can result in infection and result in the fruit being unmarketable.

Flea beetles feeding on young, fall planted, cole crops. F. Becker photo

Flea beetles continue to feed on several crops including tomatoes and cole crops. The feeding on tomato plants is not of major concern mostly because the damage I am seeing is on the lower leaves. The damage on cole crops is of more concern due to the areas of the plants being damaged. The flea beetles are feeding on young tender leaves on kale plants as well as causing heavy damage on young plantings of broccoli and cabbage. Too much damage at this point can stunt the plants growth and result in reduced yield.

The trap counts for sweet corn pests in Wayne County are overall down. Sweet corn growers should be keeping an eye out for army worm damage as we have had reports of high fall army worm trap counts as well as damage that was being done by the yellow striped army worm. More on recent trap counts

Vegetable Diseases

            Downy Mildew is in Wayne and Medina counties and likely in surrounding counties as well. Cucumber growers need to be spraying for downy mildew.

Powdery mildew can be just as destructive on squash as downy mildew is on cucumbers. I have been finding powdery mildew consistently in younger squash plantings. Unfortunately, the earlier the plant is infected with powdery mildew, the shorter the life span of the plant. With an infected plant having a short life span, the yield for the plant can also be expected to decrease.

Smut is especially prevalent on sweet corn this year. Smut is more common during hot and dry weather, especially when followed by a heavy, warm rain. This year has been the perfect year for prime smut infection and growth.

In some pepper fields, there has been a few spots of anthracnose found on the fruit. Anthracnose typically does not affect the pepper foliage; however, the pepper fruits are highly susceptible to infection from the disease. Peppers develop large sunken lesions with pink to orange colored spores. This disease can be found typically on the lower sets of fruit, where they are more likely to be splashed with soil from heavy rains.

Fruit Pests

Spotted wing drosophila have been active in small fruits for some time, but with peaches starting to ripen, the SWD can and will target the peaches as well. I have started to find peaches that have SWD larva feeding just under the skin.

SWD can also do damage to grapes. This week I started to find berries in grape clusters that were soft or looked poorly. Just under the skin of these grapes I found SWD larva feeding and moving around. Many grapes are ripening and getting close to harvest so anyone with grapes should consider treating for SWD.

Brown marmorated stink bug trap with adults and nymphs present. F. Becker photo.

Stink bugs can also do a lot of damage to fruit crops this time of year. We have traps out for the brown marmorated stink bug, which will help us monitor its population, however, I am already finding some stink bug damage on peaches and apples. This damage appears as a discolored depression in the skin with corking of the flesh all the way up to the skin. This damage can occur anywhere on the apple.

Fruit Diseases

            Overall, disease pressure has been fairly limited this year. Hot and dry conditions have prevented favorable conditions needed for disease development. As fruit continues to ripen and be harvested, we continue to move forward through the growing season without many disease issues in our area.

Some grape varieties are nearing harvest. At this point, there should be no significant disease concerns, especially so close to harvest. The same goes for orchard crops.

If you are doing any final treatments for fruit diseases, pay close attention to the PHI on the product label. The pre-harvest interval determines how long after you applied that product that you may harvest the crop. This is especially important to pay attention to as many varieties of orchard crops as well as grapes are maturing and nearing harvest.

Notes on Downy Mildews – Cucurbits and Basil

Downy mildew on cantaloupe

Downy mildew has been reported in several Northern Ohio counties: on cucumbers in Huron, Medina, Sandusky, Seneca, and Wayne counties, and also on cantaloupe in Sandusky County. There have been also several reports of bacterial diseases in cucumbers (angular leaf spot) and pumpkins (bacterial spot) – these diseases can be mistaken for downy mildew. You can find information on cucurbit downy mildew management in my post here.

Downy mildew on basil

We have also found basil downy mildew in our sentinel plot in Huron County. Basil downy mildew management recommendations for gardeners and commercial growers can be found here.

Optimizing Plant Spacing (Population) and Seasonal Nitrogen Rates in Grafted Watermelon Production

Data collection on fruit taken from two “grafted watermelon” experiments being completed at the OARDC in Wooster,OH has started. These experiments were outlined in VegNet posts on June 6 and July 11 and they are described in the image below, too.

Harvest 1 occurred on 8/19/20 with ‘Jade Star’ fruit harvest and analysis. The first harvest of ‘Fascination’ will be the week of 8/24 and a second harvest of each variety from both experiments is also planned. We assess the maturity of each fruit and its readiness for harvest using these criteria: a) yellow belly, b) dry vine tendril, c) developing longitudinal ridges, and d) white stripes brightening and widening (‘Fascination’). Occasionally, fruit weighing less than 8 lb meet one or more of these criteria, so they are harvested and photographed along with all other fruit from the same plot. Fruit weighing less than 8 lb are later separated from the group of fruit weighing more than 8 lb (marketable). In all pictures below, fruit are shown on a blue tarp slightly larger than 7 ft wide x 4 ft tall.

Pictures below are representative of what was observed in replicates 1-3 but conclusions should not be drawn from them. Data from Harvest 2 are needed to complete the picture and all data from 2020 must be analyzed along with data from previous years of the research (2018, 2019). On 8/19/20, in the “density” study, we observed that all four plots containing grafted plants produced a total of 12 fewer fruit than the four plots containing grafted plants at an in-row plant spacing of four feet. However, the situation was reversed at an in-row plant spacing of five feet since the four plots containing grafted plants produced a total of thirty-five more fruit than the four plots containing ungrafted plants at the same spacing.

The last planned fertilizer application (fertigation) in the “fertility” study was completed on 8/21/20. Two days before, the number of fruit taken from all twelve plots containing grafted plants was greater than the number of fruit taken from the twelve plots with ungrafted plants, regardless of seasonal nitrogen (N) rate. The difference in fruit number was greatest, moderate, and least at 75%, 100%, and 50% of the normal N rate, respectively. The pictures below are an example of the difference in fruit number at the standard N rate developed for watermelon production using ungrafted plants.

The experiments are being completed with USDA-SCRI program support and we look forward to sharing the results when the work is complete. In the meantime, please contact us (kleinhenz.1@osu.edu; 330.263.3810) for more information.

Cercospora “Frogeye” Leaf Spot of Pepper

Frogeye lesions on pepper leaves (photo by M. Netz)

Frogeye leaf spot, caused by the fungus Cercospora capsici, has distinctive symptoms on leaves, stems and peduncles of pepper and eggplant. Lesions are circular or oblong, tan in the center and surrounded with a necrotic border and often yellowing tissues. As the lesions expand, concentric rings may be present. The lesions resemble a frog’s eye, hence the name.

Several farms in Northwest Ohio have recently reported this disease in peppers.  It has not been common in this area, and likely appeared due to the unusually hot weather this growing season.  Frogeye leaf spot is favored by warm, wet conditions.  Cercospora produces spores in the lesions that are dispersed by air, rain, overhead irrigation and tools and equipment.

Frogeye lesions and chlorosis on pepper leaves (photo by M. Netz)

This disease is managed by a combination of cultural practices and fungicide applications. Cercospora survives at least a year on crop residue, so residues should be plowed under to hasten decomposition. Drip irrigation should be used if possible. Fungicides typically recommended are Quadris, Quadris Top, Aprovia Top, Cabrio and mancozeb. Fungicide applications should be alternated according to fungicide mode of action (FRAC code) to reduce the development of fungicide resistance.

Update on worms in sweet corn and peppers

Last Saturday, I wrote that the corn earworm population was lower than usual for this time of year, but then two days later, last Monday, our traps in Columbus had the highest catch of the year. Populations of corn earworm are still moderate in size, not yet in the high range, but sweet corn fields that are silking will be at risk of infestation if control measures are not taken. As the local large acreage of field corn begins to dry down, the relatively small fields of sweet corn will be more attractive to the increasingly larger number of moths in the area. Sweet corn and pepper growers who have their own traps are encouraged to check the traps several times per week. Growers who do not have their own traps should check our website where trap reports are published.

Trap reports for corn earworm and European corn borer from several Ohio locations can be found using this link: https://docs.google.com/spreadsheets/d/10gh3rHahdxLKkXQapGyEPxWsjHYRmgsezOoFHnwtyEo/edit#gid=0

More information about trap-based insecticide spray scheduling for sweet corn is available using this link: http://u.osu.edu/pestmanagement/crops/swcorn/ .

-Celeste Welty, Extension Entomologist

 

Wayne County IPM Notes for August 9 – August 15

Wayne County IPM Notes

Vegetable Pests

Aphids feeding on the under side of a pumpkin leaf. F. Becker photo.

In many crops, I am starting to see aphids feeding on the underside of the leaves. Most consistently, I have seen this in pumpkins. The aphids cause direct damage to the leaves via their feeding, but they can also cause other issues such as the sooty mold that happens as a result of their exudate known as honeydew. Additionally, aphids can potentially transmit viruses from plant to plant.

Flea beetles are still a problem in both young, recently transplanted crucifer crops, as well as cabbage and kale either in harvest or near harvest. Feeding damage from flea beetles on the younger crops can cause stunting and reduced yield. This damage can be especially impactful on heat stressed transplants. The foliar feeding being done on maturing crops can affect the visual appearance of the crop and may result in a less desirable product.

In cucurbit crops, the main pests causing problems are cucumber beetles and squash bugs. The cucumber beetle and their larvae can be found causing damage to both pumpkin and melon skins throughout the fields. Squash bug eggs are starting to hatch, and I am starting to find various stages of nymphs out in pumpkin fields and squash plantings. Currently most feeding is being done on the leaves; however, the focus of the feeding can shift to the fruit and cause scarring to the skin resulting in decreased marketability. The squash bug has also been found to be the vector of a bacterium that causes the disease Yellow Vine Decline.

Vegetable Diseases

            Downy Mildew is in Wayne and Medina counties and likely in surrounding counties as well. Cucumber growers need to be spraying for downy mildew.

Sweet corn ear with large smut galls. F. Becker photo.

As tomato plants put on more foliage, the airflow between plants is restricted, which results in higher moisture environments within the plants. This high moisture environment is conducive for several fungal infections such as Septoria leaf spot and early blight. Both of these diseases are currently becoming more prevalent in field tomato plantings. This is also happening after a few heavy rains where soil was splashed onto the lower leaves.

Powdery mildew can be just as destructive on squash as downy mildew is on cucumbers. I have been finding powdery mildew consistently in younger squash plantings. Unfortunately, the earlier the plant is infected with powdery mildew, the shorter the life span of the plant. With an infected plant having a short life span, the yield for the plant can also be expected to decrease.

Sweet corn growers have been finding a lot of smut on the ears and sweet corn plants. Smut is more common during hot and dry weather, especially when followed by a heavy, warm rain. This year has been the perfect year for prime smut infection and growth.

Fruit Pests

Japanese beetles are still feeding in nearly every crop that I am scouting. They are doing damage to apple leaves, peach leaves, grape leaves, blueberry leaves and blueberry fruit. It is important to watch the populations of Japanese beetles because they can transition from only feeding on the leaves to doing significant damage to the fruit.

In orchards I am seeing an increase in spider mite populations. This includes two spotted spider mites and European red mites. These mites, while not causing major damage initially, can cause significant damage over prolonged periods of feeding.

Spotted wing drosophila have been active in small fruits for some time, but with peaches starting to ripen, the SWD can and will target the peaches as well. I found a handful of ripe peaches this week with soft spots on them. Upon peeling the skin back, I could clearly see several SWD larva feeding in the peach.

There was a short time of limited codling moth and oriental fruit moth activity, however, the traps again picked up high counts of both moths this week.

Fruit Diseases

            Overall, disease pressure has been fairly limited this year. Hot and dry conditions have prevented favorable conditions needed for disease development. As fruit continues to ripen and be

Some grape varieties are nearing harvest. F. Becker photo.

harvested, we continue to move forward through the growing season without many disease issues in our area.

Apple and peach growers should continue their spray programs to manage fruit rots and diseases such as flyspeck and sooty blotch in apples and brown rot in peaches. Alternaria leaf blotch can be found on some apple trees right now. This can be made worse by red mite infestations. With high populations of mites and the leaf blotch, severe defoliation can occur.

Grapes should be starting to get some color to them as the clusters are starting to increase in size. Although symptoms of black rot may be showing up on untreated grapes, it is too late to do anything.  Growers with varieties of grapes that are not resistant to downy mildew should consider a spray program. Grape growers should also keep an eye out for powdery mildew, as this is the time of year when powdery mildew is typically found on grapes.

Worms in sweet corn and peppers

Almost every year at this time, we see a surge in activity of corn earworm, mostly from large numbers of corn earworm moths that blow up on weather fronts from the southern USA. This year has been unusual so far, in that we are seeing only a slight increase in corn earworm moths, and not yet seeing a large surge. This could change at any point, but it means that for now, growers should be able to get good control of worms in silking corn using insecticide at a less intense schedule than usual for August. At our Ohio sites that reported trap catch this past week, there were 0 to 9 moths in the Scentry type of pheromone trap. The recommended spray interval during hot weather (high >80 F) is every 4 days when traps are catching 3.5 to 7 moths per week, or every 3 days when traps are catching 7 to 91 moths per week, as shown in the table below.

   Spray schedule for silking sweet corn.

More information about trap-based spray schedules is available using this link: http://u.osu.edu/pestmanagement/crops/swcorn/ .

We have observed in our Ohio insecticide trials that in years when corn earworm moths are abundant, pyrethroid insecticides such as Warrior, Brigade, Mustang Maxx, Baythroid, and permethrin do not provide very good control even when used at the maximum labelled rate, however in years when corn earworm moths are not very abundant, pyrethroids can provide very good control, if used at the maximum labelled rate.

The other worm pest that is very important during August of most years is the European corn borer. Although this pest has been less abundant during the past 10-15 years than previously, throughout the Midwest, it still can be a key pest of peppers and sweet corn in late summer. We usually see its first generation larvae in June, and its second generation larvae in August. We expect to see larvae once we see the adult moths present, as can be detected by pheromone traps and blacklight traps. The first moths are usually found in traps in the last week of July. However, this year, we are seeing very few moths through mid-August. They are still likely to appear, but they are running a few weeks later than usual.

Trap reports for corn earworm and European corn borer from several Ohio locations can be found using this link:  https://docs.google.com/spreadsheets/d/10gh3rHahdxLKkXQapGyEPxWsjHYRmgsezOoFHnwtyEo/edit#gid=0

-Celeste Welty, Extension Entomologist

Plectosporium Blight of Pumpkins, Squash

White, diamond-shaped lesions of Plectosporium blight on pumpkin vine (photo by Francesca Rotondo)

We’ve had several reports this week of Plectosporium blight appearing in pumpkins in Ohio. Sometimes also called white speck, this is a disease of pumpkins and squash caused by the fungus Plectosporium tabacinum. The symptoms on vines, leaf petioles and veins on the back of the leaves are small, white and diamond-shaped lesions; on fruits the lesions are also small and white, generally

Advanced symptoms of Plectosporium blight on pumpkin vine (photo by Brad Bergefurd)

round. Under favorable environmental conditions (rainy, moderate temperatures) the lesions can coalesce, and the affected tissues appear white and become brittle. Plectosporium produces spores in the lesions that are dispersed long distances by the wind. The fungus survives in soil associated with plant debris for several years.

Plectosporium blight management requires an integrated approach that includes crop rotation, cultural practices and fungicide applications. Although pumpkin and squash varieties vary somewhat in susceptibility to this disease, none are resistant. In a study we conducted in 2018 at the OSU South Centers in Piketon, OH, the varieties ‘Hulk’, ‘Cronus’, ‘Warty Gnome’ and ‘Bayhorse Gold’ had less Plectosporium blight than other varieties in the trial.

Plectosporium blight lesions on pumpkin vine and handle (photo by Brad Bergefurd)

 

Plectosporium blight management:

  1. Rotate out of cucurbits for 2-3 years.
  2. Choose a site with good air circulation to allow plants to dry quickly.
  3. Use drip irrigation instead of overhead irrigation.
  4. Scout fields, looking for diamond-shaped lesions on leaf veins, vines and petioles within the canopy; if present, apply fungicides on a 7-day schedule.
    • Chlorothalanil (e.g. Bravo), the strobilurin fungicides such as Quadris, Quadris Top and Pristine, and Topsin M are the most effective fungicides against Plectosporium blight, but do not fully control the disease.  It is important to get good coverage of the fungicides well into the canopy.  Use high water volumes – at least 40 gal/acre. Strobilurin fungicides have translaminar activity and move through the leaves, improving coverage.
  1. After harvest plow down the crop residue to encourage rapid decomposition.

 

Wayne County IPM Notes for August 2 – August 8

Wayne County IPM Notes

Vegetable Pests

Yellow-striped army worm that was found down in the whorl of a V8 corn plant. F. Becker photo.

Army worms have continued to do damage to sweet corn plants. The damage I am finding is typically being done in the whorls on the young tender leaves. Another sign of army worm feeding is large areas along the leaf edges that have a ragged appearance.

Flea beetles continue to be a problem in both young, recently transplanted crucifer crops, as well as cabbage and kale either in harvest or near harvest. Feeding damage from flea beetles on the younger crops can cause stunting and reduced yield. This damage can be especially impactful on heat stressed transplants. The foliar feeding being done on maturing crops can affect the visual appearance of the crop and may result in a less desirable product.

In cucurbit crops, the main pests causing problems are cucumber beetles and squash bugs. The cucumber beetle and the larva can be found causing damage to melon skins throughout the fields. Squash bug eggs are starting to hatch, and I am starting to find various stages of larva out in pumpkin fields and squash plantings. Currently most feeding is being done on the leaves; however, the focus of the feeding can shift to the fruit and cause scarring to the skin resulting in decreased marketability. The squash bug has also been found to be the vector of a bacterium that causes the disease Yellow Vine Decline.

Vegetable Diseases

Early blight on a tomato leaf. F. Becker photo.

As tomato plants put on more foliage, the airflow between plants is restricted, which results in higher moisture environments within the plants. This high moisture environment is conducive for several fungal infections such as Septoria leaf spot and early blight. Both of these diseases are currently becoming more prevalent in field tomato plantings. This is also happening after a few heavy rains where soil was splashed onto the lower leaves.

Downy Mildew is in Wayne and Medina counties and likely in surrounding counties as well. Cucumber growers need to be spraying for downy mildew.

Powdery mildew can be just as destructive on squash as downy mildew is on cucumbers. I have been finding powdery mildew consistently in younger squash plantings. Unfortunately, the earlier the plant is infected with powdery mildew, the shorter the life span of the plant. With an infected plant having a short life span, the yield for the plant can also be expected to decrease.

Fruit Pests

In orchards I am seeing an increase in spider mite populations. This includes two spotted spider mites and European red mites. These mites, while not causing major damage initially, can cause significant damage over prolonged periods of feeding.

Japanese beetles are still feeding in nearly every crop that I am scouting. They are doing damage to apple leaves, peach leaves, grape leaves, blueberry leaves and blueberry fruit. It is important to watch the populations of Japanese beetles because they can transition from only feeding on the leaves to doing significant damage to the fruit.

After a few weeks of high numbers in both oriental fruit moth and codling moth traps, the trap counts have started to back down a bit.

Fruit Diseases

            Overall, disease pressure has been fairly limited this year. Hot and dry conditions have prevented favorable conditions needed for disease development. As fruit continues to ripen and be harvested, we continue to move forward through the growing season without many disease issues in our area.

Grapes should be starting to get some color to them as the clusters are starting to increase in size. Although symptoms of black rot may be showing up on untreated grapes, it is too late to do anything.  Growers with varieties of grapes that are not resistant to downy mildew should consider a spray program. Grape growers should also keep an eye out for powdery mildew, as this is the time of year when powdery mildew is typically found on grapes. “Managing Grape Diseases” 

Apple and peach growers should continue their spray programs to manage fruit rots and diseases such as flyspeck and sooty blotch in apples and brown rot in peaches. Alternaria leaf blotch can be found on some apple trees right now. This can be made worse by red mite infestations. With high populations of mites and the leaf blotch, severe defoliation can occur.