OSU Extension Fruit & Vegetable Report – July 19th, 2024

This article was originally posted in the Fruit, Vegetable, & Specialty Crop Newsletter. To view the original article, click HERE. 

Vegetables

Spider mite flares ups have started to cause damage in watermelon fields. The observed infestations are severe and resulting in rapidly declining plants. Spider mite flare ups are not uncommon during hot and dry conditions, which are currently being experienced by some areas of the state. Frequent or heavy rains typically wash spider mites off of the plants. There are also several natural enemies that can help hold spider mite populations in check such as lacewing larvae, predatory mites, predatory thrips, and minute pirate bugs. Spider mites are typically found in the underside of the leaves. The visual symptoms of their feeding are often observed on the top side of the leaves as the mite feeding damages the cells in the leaves and results in yellowing, stippling and eventually necrotic areas and foliar dieback. When utilizing insecticides for insect control, there is a potential to wipe out beneficial insect populations, allowing for mite flare ups to occur. Also, if you do need to make an application to control mites, make sure you are using a miticide that is labeled for use against the mite species that you are finding and that it has activity on all life stages of the mites. It is common to have all stages of the mites life cycle present at one time, especially as populations increase and generations advance rapidly.

Spider mite webbing and damage on melon leaves. Photo by Frank Becker, OSU Extension. 

Severe groundhog damage is being reported in various vegetable crops, including those grown at OSU research facilities. Fencing can be used, but the fence must be semi-buried to prevent the varmints from just burrowing underneath it. Trapping is the other most common option. For more information, check out the two articles below:

Animal Damage Management: Groundhogs – Purdue Extension

Ecology and Management of the Groundhog – Rutgers

There has been a resurgence of flea beetles as the second generation descends on the newer planting of cole crops. Squash bugs, squash vine borer, powdery mildew, and downy mildew are all damaging cucurbits. A flare up of cucumber beetles and bacterial wilt is also occurring. Corn smut is affecting some sweet corn plantings. Oftentimes, desirable and productive varieties may have poor disease resistance to pathogens like corn smut. Cultural practices for reducing incidence of corn smut in your field includes minimizing mechanical damage to plants that provides entry points for pathogens, as well as other standard practices like crop rotation, timely destruction of crop residues, and keeping nutrient levels balanced.

Bacterial diseases are also being reported in peppers. Anthracnose was diagnosed on cucumbers. Fusarium and verticillium are occurring in tomatoes, and Fusarium is also being reported in melons. Bacterial spot is popping up on tomatoes due to the recent heavy rains.

Early anthracnose infection on cucumber leaves. Photo source: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org

Fruit

It has been a good year for peaches and plums in Ohio. It has also been an early season – Dr. Diane Miller remarked that the variety sequence will be slotted earlier than normal this year. Fire blight risk has decreased considerably. White apple leafhopper has been observed causing moderate feeding damage in several orchards. White apple leafhoppers have piercing-sucking mouthparts that cause yellow-whitish stippling on the leaves. Both adults and nymphs can be found currently when scouting apple trees.  At this point in the season, try to target insecticide applications when you get 3 leafhopper nymphs per 25 leaves/tree. Neonicotinoids are effective against this pest (e.g., Belay (Clothianidin), Actara (Thiamethoxam), Assail (acetamiprid)). Be mindful of the pre-harvest interval since applications of these products at higher rates will increase the interval.

White apple leafhoppers. Photo by Frank Becker, OSU Extension. 

High mite pressure has been reported in high tunnel raspberries. Are beneficial mites sufficient for mite control in high tunnels or greenhouse settings? It depends on environmental conditions – overly high temperatures can be detrimental for predatory mite survival which causes diminished levels of control. Phytophthora root rot has been reported in raspberries.

Photo by Thomas Becker, OSU Extension. 

With blueberry season in full swing and blackberry season about to get underway in much of the state, Spotted Wing Drosophila is a pest that small fruit growers need to have on their radar. Drosophila suzuki or spotted wing drosophila (SWD) is a fruit fly pest of small, soft-bodied fruits. To be able to identify the adults, many extension educators and specialists have to use a stereo microscope. It would take a hand lens at the very least, and even that may not be enough, as the key identifying features are quite small. Interestingly enough, only the male SWD has the characteristic spotted wing. The wings of the males are mostly clear, with one lone spot near the tip of each wing. Another ID tip for the males that is a bit more difficult to see is the presence of 2 black bands on their front legs. These bands are actually patches of hairs called sex combs. The main identifying feature on the females is their unique ovipositor. The ovipositor is the structure that female insects use to lay/deposit their eggs. For SWD, their ovipositor is lined with two rows of dark colored serrations or teeth. These serrations allow the female SWD to cut into ripening or just ripe fruits. This is different from many of the other fruit fly species we are used to, that infest over ripe or rotten fruit.

Photo by Thomas Becker, OSU Extension. 

The fruits of primary concern are raspberries, blackberries, grapes, cherries, and strawberries. In Ohio, it seems that strawberries are pretty well done by the time that we start to detect SWD. Generally, first detection occurs when blueberries and raspberries are coming into season. Extension Educators and specialists around the state have SWD traps out to monitor pest populations. First detection is a critical aspect of managing this economically significant pest. The tolerance for damaged or wormy fruit is extremely low. The threshold for management to be implemented is one adult SWD in the trap. According to trapping data collected this year, first detection in the state occurred mid to late June.

Once SWD is present in the environment, there are a couple of ways to try and manage it. You can start with cultural management by harvesting as thoroughly as you can and disposing of cull fruits. While it might be time consuming and require some extra labor, managing those culls could be worth the time and effort if it means you are removing a host site for the SWD. In addition, the more quickly you can get the fresh fruit off the plants, the less chance the flies have to lay their eggs in them. There are also some recommendations out there for physical exclusion. Berries under plastic, like a high tunnel for example, or under a fine mesh can reduce the number of adults gaining access to the fruit. However, there are some micro-climate considerations to keep in mind. Of note are air movement and access for pollinators (if needed). A fact sheet from Penn State University discusses the potential for biological control. There is apparently work being done to introduce a parasitoid wasp that targets SWD, but this work is still in its early stages. There are also multiple chemical options as well. You can find up-to-date chemical recommendations by checking in the Midwest Fruit Pest Management Guide or contacting your county Extension Educator. Penn State also has a 4-part fact sheet series on SWD with lots of good information.

Resources: https://extension.umn.edu/yard-and-garden-insects/spotted-wing-drosophila#using-insecticides-2403912

https://extension.psu.edu/spotted-wing-drosophila-part-1-overview-and-identification

Orange Rust is a frequent problem on blackberries in Ohio. It is no exception this year. Dr. Gary Gao got a grant from Ohio Vegetable & Small Fruit Research & Development Program this year to evaluate the orange rust disease resistance of two new blackberry varieties from University of Arkansas. The varieties are Caddo and Ponca. A few plants were planted between the orange rusted blackberry plants. In addition, Ryan Slaughter and Dr. Pengfei Wen, a visiting scholar from Shanxi Agricultural University, helped inoculate the new plants with orange rust infected plant leaves. So far, Caddo and Ponca have not shown any symptoms of orange rust. This is a pretty crude field trial. Gary also asked growers about their experiences with Caddo and Ponca.

Photo by Dr. Gary Gao.

Ouachita, a leading blackberry cultivar for Rotatable Cross Arm training system, is reported to have shown good tolerance for orange rust. Growers look for orange rust resistant varieties to extend the harvest season. Caddo started its initial harvest a few says before Ouachita and a few days after Natchez. Caddo’s peak harvest season is also earlier than Ouachita. However, Caddo yield is quite lower than that of Ouachita based on observations in Ohio.

Sweet-Ark™ Ponca is an early ripening blackberry cultivar with extremely sweet flavor. It ripens at about same time as Natchez. Some of the growers in Ohio have planted Sweet-Ark™ Ponca Blackberries. It is hard to know if this variety will be a good fit for your blackberry operation. However, a blackberry variety with super sweetness may be worth consideration on a small scale. Sweet-Ark™ Ponca blackberry may now be as productive as Ouachita, but early fruit, sub acid and super sweetness may warrant a small planting. Sweet-Ark™ Ponca blackberry is reported to be resistant to orange rust. Hopefully, we will get a better idea about its orange rust resistance after we wrap up our trial.

In addition to planting orange rust resistant blackberry cultivars, a fungicide spray needs to be implemented. Here is an informative article from University of Maryland:  https://extension.umd.edu/resource/orange-rust-bigger-problem-usual-year-brambles/.   Growers can also follow the following link for detailed a spray schedule for blackberries: https://ag.purdue.edu/department/hla/extension/_docs/id-465.pdf