2022 PA Vegetable and Berry Current Issues for August 2

As we turn the corner towards fall, remember that long dew periods can lead to more favorable conditions for disease, even if the daytime temperatures are in the upper 80s and 90s. Diseases can continue to progress at night with the cooler temperatures and more extended periods of leaf wetness.

Field Production

Most reports this season have been on cucumber, with a few on cantaloupe (clade 2; see map on the left), while information on other hosts (clade 1) is only from as far north as Tennessee. Reports of downy mildew on cucumber continue to increase with new reports in Centre, Mifflin, Dauphin, and Lehigh Counties. Regionally, there have been recent reports in Michigan, West Virginia, Virginia, and northern New Jersey again, all on cucumber. Powdery mildew continues to be reported on pumpkin and zucchini.

Figure 2. Clade 2—map on left, the majority of reports this season have been on cucumber with a few on cantaloupe. Clade 1—map on the right, reports on other hosts, are only from as far north as Tennessee.

Ozone damage is reported in some cucurbit crops, although it can also damage other crops such as snap bean. It can cause small white spots on the leaves where stomates were open, allowing entry into the leaf. It is most common under hot and humid conditions with limited air movement. See the article Ozone Damage to Cucurbit Foliage Common in Maryland by Jerry Brust at the University of Maryland for more information.

Figure 3. Ozone damage on a pumpkin. Photo: PA crop consultant

Phytophthora blight is being confirmed on pepper and cucurbit crops on several farms across all major growing regions in the state. If the pathogen is present, it does not take much water for infection to occur, especially on fruit that are in contact with the ground. In areas where Phytophthora is known to be a problem, be careful when sharing equipment between fields, even under dry conditions. The pathogen can survive in the soil without a host and can easily be moved between fields and farms.

Significant wildlife damage, especially from deer, is being reported across many state regions. Exclusion fencing is a recommended best practice, especially with crop establishment costs rising. One recommended system is a two-tiered fence system. The concept is to have two single-line electric fences separated by 5 ft, with the outer line at approximately 2 ft off the ground and the inner line 5 to 10 ft from the ground. Growers could start with a one-tier system and bait with peanut butter and aluminum foil before deciding on establishing a two-tier system. See this article titled Managing Deer Damage Using a Two-Tiered Fence System from Zack Snipes at Clemson, which includes the estimated cost of fencing an acre. The PA Game Commission Agricultural Deer Control (Red Tag) Program may be another option that allows for a special permit for deer control related to agricultural depredation. 

Berry Crops

Spotted wing drosophila is the main berry problem right now. We do have some good news on this front: limited initial releases of a parasitoid wasp will be taking place this week and into the fall in PA (and other states). Many thanks to Xingeng Wang, Kim Hoelmer, and Amanda Stout at the USDA Beneficial Insects Introduction Research Unit in Delaware for raising the wasps and sending them to us, Kelly Hamby at the University of Maryland for her advice and getting us off the ground, and Kent Daane at the Univ. of California for handling the paperwork so we could obtain a permit for release. None of this would be happening without their hard work and efforts. We do not yet know whether the wasp will successfully establish and overwinter here, and it will likely only provide partial control if it does. Still, at least this is a step in the right direction towards making SWD less problematic than it currently is.  

This is the time of year when rednecked cane borer damage may be seen on raspberry plants – look low on the cane for a swelling about a foot from the ground. If you see canes with this type of damage, remove the entire cane at ground level and destroy it. Raspberry cane borer is another common pest where damage can be seen now. With this pest, at first, you will see wilted tips with two lines of puncture marks just below the wilted area and a hole between the two lines. The tip dies and often breaks off, and the cane will send out lateral branches later. If this pest is present, remove the cane below the damaged area, making sure you do not see a hole from the borer tunneling downwards. If you do, cut the cane lower to be sure that you remove the borer and, again, destroy the pruned-out canes so the borer adults do not simply hatch out somewhere else nearby.

Figure 4. Raspberry cane borer punctures (red square) an egg is laid between the two lines of punctures. Photo: K. Demchak, Penn State

There are also other types of borers, some of which are generalist feeders. Their tunnels only extend into the cane for a couple of inches below the tip, unlike those of other borers, which extend throughout much more of the cane. Still, it is essential not to confuse borer damage with holes made in tipped raspberry or blackberry canes by solitary bees laying eggs. These bees are attracted to the soft pith in the center of the cane.

Figure 5. This hole made in the pith of a tipped cane is from a solitary bee that had hatched. Photo: K. Demchak, Penn State   

The yellow-necked caterpillar (Figure 1) is out and about, defoliating blueberry plants once again. This could be the culprit if leaves seem to disappear from your bushes overnight. Because the caterpillars are located together, physical removal is relatively easy. It is the best control method, but by the time you notice the damage, they have usually moved on to different plants—so look around if you don’t spot them at first.