The annual spring meeting of the Southwest Indiana Melon and Vegetable Association will take place on Friday, March 8, 2019 at the French Lick Resort and Casino, 8670 West State Road 56, French Lick, IN 47432. Registration starts at 8:30 a.m. EST. Topics include: watermelon production in Georgia, food safety update, irrigation of cucurbits, pollinator safety, health of watermelon transplants, and putting the sprayer on the road. Those who attend the afternoon session, from 1:30 until 3:30 will receive Private Applicator Recertification Credit (PARP). Registration is $15 and includes lunch. Individuals who want PARP certification should bring $10. Please direct questions to Dan Egel, (812) 886-0198; egel@purdue.edu.
Dan Egel
This disease was identified on a long Asian cucumber growing in a high tunnel in Mid-June in Knox County. The first symptom noted was wilting of the cucumber plant. Upon closer examination, a light, gray necrosis was observed on the lower portion of the plant. In Figure 1, you may notice dark spots in the necrotic area. These symptoms, plus the resin-like drops on the stem might look like gummy stem blight. However, a look under the microscope revealed fungal structures and spores that were not from the gummy stem blight fungus. Plus, gummy stem blight is rare in a greenhouse situation where there is little moisture. When we isolated for a fungus, we found numerous micro-sclerotia. The sample was sent up to campus to confirm that the fungus was Macrophomina phaseolina, causal agent of charcoal rot. The charcoal rot fungus has many hosts and the fungus is not new[Read More…]
The following two articles describe two vegetable diseases new to Indiana that were recorded this past season. While neither of the disease reports are from severe outbreaks, it might be a good idea to become familiar with what may become a new disease situation. Target spot of tomato was identified from a tomato plant growing in a high tunnel in early July in Carroll County. At first glance, the disease appears to be early blight (Figure 1). Target spot may cause necrotic lesions in a concentric pattern. Although target spot may cause lesions on fruit, we did not observe such lesions. After incubation of the leaves, spores that appeared to be Corynespora cassiicola, causal agent of target spot were observed. This fungus was isolated in our lab and the identity of the fungus was confirmed by sequencing on campus. This is the first report of target spot of tomato in Indiana.[Read More…]
With the start of pumpkin harvest, it is a good time to review important considerations for harvest and postharvest storage of pumpkins and winter squash (butternut, acorn and hubbard squash etc.). Pumpkin and winter squash should be harvested fully mature to reach their optimal quality and fulfill their potential for long shelf lives. Characters indicating fruit maturity include loss of rind surface gloss, ground spot yellowing, and hardening of the skin to the level that it is resistant to puncture with a thumbnail. Except for some striped varieties, mature fruit should have solid external color. If fruit have to be harvested pre-mature because of plant decline, these fruit won’t store as well as mature fruit. The best practice is to harvest the fruit as soon as they are fully mature and then store under proper conditions. If mature fruit are left attached to the vines, it increases the chance of[Read More…]
Several pumpkin growers have asked me when to stop managing for pumpkin diseases. That is, when should a pumpkin grower stop applying fungicides? I cannot provide a definitive answer for this question; every grower will have to make his or her own decision. Below, however, are some factors to consider. Estimate the crop yield-walk through the field and evaluate the yield of pumpkins that are ready to harvest. Be sure to only consider fruit of marketable quality. If the yield is at or above what is expected, it may be time to put the sprayer away. Estimate when harvest will take place-Pumpkins that are scheduled for harvest in the next week or two are less likely to need any fungicide treatment. A longer period to final harvest may indicate that there is time for immature fruit to ripen. For example, pumpkins that are to be picked by the consumer up to Halloween may have time to mature.[Read More…]
Before writing this article, I went back to an old article from 2015. In 2015, I had written, Plectosporium blight was more severe than normal. In 2018, I have also observed more Plectosporium blight than usual. It is not clear to me why this disease seems to be more widespread compared to recent seasons. However, it makes sense to review Plectosporium blight here. I would rank Plectosporium blight behind powdery mildew, bacterial leaf spot and Phytophthora blight in economic damage caused. The occurrence of this disease is usually sporadic. However, when it occurs, it can cause yield loss if left uncontrolled. Plectosporium blight can be recognized from the light tan spindle shaped lesions on stems and leaf petioles (Figure 1 and 2) Lesions on leaves may be dimple like. Lesions may also occur on the fruit (Figure 3), although these symptoms are less common. Yield loss is most often caused[Read More…]
Cucurbit downy mildew has been observed on cucumber in LaPorte County and LaGrange Counties, in northern Indiana and Knox County in the southwest. Downy mildew of cucurbits has also been reported in Kentucky and Michigan. See this article (https://vegcropshotline.org/article/cucurbit-downy-mildew/) in the last Hotline issue about details of downy mildew. Whether growers manage for downy mildew at this late date will depend on when last harvest is anticipated. Cantaloupe and watermelon growers who plan a final harvest at or close to Labor Day should not have to apply any specialized fungicides. Pumpkin growers often start to harvest in early September. Such growers will have little to worry about from downy mildew. However, cucurbit growers who anticipate harvesting fruit that is still developing may want to consider products that were discussed in the last issue of the Hotline. Remember, downy mildew doesn’t affect the fruit directly. Downy mildew affects fruit development by[Read More…]
In the fall of 2015, I wrote an article for the Hotline about Cercospora leaf mold of tomato since this disease had been observed twice in the 2015 season. I wrote that Cercospora leaf mold was normally a subtropical disease. There have been several observations of Cercospora leaf mold on tomato in Indiana this year. I’m still not certain of the importance of this disease, but this article will compare Cercospora leaf mold and leaf mold of tomato. Leaf mold of tomato is caused by Passalora fulva and is common in Indiana, especially in high tunnels where the high relative humidity favors this disease. Cercospora leaf mold is caused by Pseudocercospora fuligena and is more common in the warm, humid climate of the tropics or subtropics than in the Midwest. Both diseases cause chlorotic (yellow) lesions which are visible on the upper side of the leaf. The chlorotic area caused by[Read More…]
This disease was confirmed in Indiana recently. Cercospora blight initially causes small, oval, gray to tan lesions with red borders (Figure 1). If a 10X hand lens is used, dark flecks within the lesions may be observed; these flecks are where the spores of the causal fungus are produced. Severe infections may cause entire ferns to turn yellow or brown. Cercospora blight may cause reduced vigor and yield of spears the next spring. The causal fungus overwinters on fern residues left on the soil. When weather in the late spring or summer becomes favorable, spores on this debris may cause disease on the ferns. High humidity in the fern canopy of 95% or higher and average temperatures of 77 to 86°F favor infection. Splashing water from rain or irrigation is important in spread of this disease. Any practice that minimizes fern debris will help to lessen the impact of Cercospora[Read More…]
Cucurbit downy mildew has been observed on cucumber in La Porte County and LaGrange Counties, Indiana. Downy mildew of cucurbits has also been reported in southern and central Kentucky. All cucurbit growers in Indiana should be scouting and managing for downy mildew. The organism that causes downy mildew of cucurbits doesn’t overwinter in Indiana. It has to be blown in every year. It is common for downy mildew to start the season in the Gulf States and migrate north with the cucurbit crops. Downy mildew apparently overwinters in northern Michigan/southern Ontario in greenhouses where cucumbers are grown year round. Therefore, downy mildew is often found in Michigan before it is found in Indiana. Many cucumber varieties have some resistance to downy mildew. For susceptible cucumber varieties or other types of cucurbits, specialized systemic fungicides will help to reduce the severity of downy mildew. Unfortunately, many of the most effective systemic fungicides for downy mildew are not[Read More…]
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