76 articles tagged "Plant Disease Management".

Downy mildew has now been observed on butternut squash, jack-o-lantern pumpkins and cucumbers in Knox County. The list of cucurbits observed in Porter County has been updated to include butternut squash and giant pumpkin. All cucurbit growers should assume that downy mildew is present nearby and may attack any cucurbit crop. However, it is not clear what affect downy mildew may have on cucurbit crops this late in the season. Pumpkin growers who expect to harvest in the next few weeks may not need to take any management steps at this time. Downy mildew affects only leaves; stems and fruit are unaffected. Indirect effects of downy mildew in fruit are unlikely to be observed in a few weeks. Another article in this Hotline issue discusses the question of when to stop managing diseases in pumpkins. If the decision is made to apply fungicides, this article https://vegcropshotline.org/article/cucurbit-downy-mildew-watch/ or the Midwest Vegetable Production Guide mwveguide.org will help to select a[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[Read More…]


Late summer is a time when vegetable growers spend much of their time harvesting produce. Many growers, however, also find it is necessary to apply pesticides. All pesticides label state a preharvest interval (PHI) on the label. This is the amount of time, in days, between the time the fruit is sprayed with a pesticides and the time it can be harvested. That is, after a pesticide is applied to a vegetable crop, a specific amount of days must pass before the fruit is harvested. This article will breifly describe how PHIs are determined, give some examples of PHIs and list a couple of questions about PHIs. I have used examples of vegetable crops and fungicides, however, the same concepts apply to apply to all pesticides and all produce. The reason the US EPA determines PHIs is to ensure that produce that is consumed does not have unsafe pesticide residues. The first step in determining a[Read More…]


Cucurbit downy mildew has been observed on cucumber and cantaloupe near Wanatah, in La Porte County, Indiana. Downy mildew has also been confirmed on cucumber in St. Joseph County Michigan, just northeast of Elkhart, Indiana as well as on processing pumpkin in central Illinois. Downy mildew of cucurbits has also been reported in southern and central Kentucky and north-central Ohio. 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[Read More…]


I have received several calls about pumpkins recently. This article will outline a few steps growers should think about to prevent diseases in pumpkins. Virus diseases – There are several virus diseases that affect pumpkins in the Midwest. The most important diseases include: papaya ring spot, watermelon mosaic and zucchini yellow mosaic virus. Aphids transmit all these diseases. Many of the aphids responsible are carried up from the south each year on winds. Therefore, aphids with virus are more common later in the summer; pumpkins planted later in the season are more likely to be affected with one of the virus diseases listed above. Plant pumpkins by about June 15 to avoid having the fruit set during the period of high virus disease pressure. Powdery mildew – It is nearly impossible to find a pumpkin vine in August without powdery mildew. However, this disease does not have to affect production. The first decision a[Read More…]


Southern blight of tomato thrives under hot, dry conditions. Usually, such conditions are more common in August than early July. However, 2016 has been relatively hot and dry in southwest Indiana. Perhaps for this reason, I have observed this disease in my own tomato plots. This article will discuss the symptoms, biology and management of southern blight of tomato. Southern blight has a wide host range affecting many vegetable, field and ornamental crops. Tomato is the most important host. The disease is caused by the fungus Sclerotium rolfsii. This fungus is related to the one that causes white mold. The first symptom one is likely to observe of southern blight is plant wilt. At the base of the plant, one is likely to notice a canker with sclerotia that may be as large as a sesame seed (Figure 1). These sclerotia are survival structures for the fungus and allow the disease to occur[Read More…]


Below, I will briefly discuss four diseases that I have observed on tomatoes recently. White mold of tomato – Perhaps the most common symptom of white mold of tomato is the light brown area on the lower stem (Figure 1). This brown area is essentially dead and will result in the wilt and death of the tomato plant above that point. Either on the outside of this dead area or inside the stem, dark, irregularly shaped fungal bodies can usually be found. These fungal bodies (known as sclerotia) are diagnostic of white mold. The fungal spores responsible for white mold are released early in the spring from a very small mushroom (several mushrooms could fit on a dime). The spores will enter a plant where tissue is dead or senescent, such as old flower petals. Fortunately, white mold, once established, will not spread from tomato to tomato plant. However, growers may observe more symptoms as later[Read More…]


I have observed leaf mold of tomato in greenhouses and high tunnels recently. This article will discuss this disease and management options. In the last issue of the Hotline, I discussed Botrytis gray mold. I noted how gray mold is favored by the cool, cloudy weather we experienced earlier this spring. The warmer and sunnier weather we have experienced more recently should favor leaf mold over gray mold. Leaf mold is caused by the fungus Passalora fulva. Cercospora leaf mold of tomato is rare in Indiana and is discussed here (https://vegcropshotline.org/article/cercospora-leaf-mold-of-tomato/). The first symptom of leaf mold one is likely to notice is a pale yellow lesion on the top side of the leaf (Figure 1). When the leaves are turned over, the fungal mold that gives the disease its name becomes evident (Figure 2). Leaf mold often becomes a problem under humid conditions (85% humidity or greater) and temperatures between 71 and 75°F, although leaf[Read More…]


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We recently published an article in the Hotline about gray mold of tomato.  That article and more details about this disease can be found here. In this short note, we want to share examples of the relationship of gray mold and tomato plant injury. In the figure 1 above, a pruning injury of tomato in a commercial greenhouse has become necrotic and a gray mold infection is starting. Figure 2 is from our research high tunnel.  In the photo, one can see where there was an abrasion, probably due to tying the plant in the greenhouse. This injury allowed the gray mold fungus to begin to grow.  Not only will this infection cause a die-back, but the spores produced may cause the disease to spread.  We clipped off this branch to stop the spread of the disease. The photo is taken outside of the greenhouse for better lighting. The lesson here is[Read More…]


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White mold of watermelon – Usually when I write about a vegetable disease it is because the disease may cause important economic loss. Once in a while, however, a disease I find is more a curiosity than a real problem. So, go ahead and read this article about white mold of watermelon. But please don’t worry about this disease. Simply, watch for these symptoms and let me know if you have questions. Readers may have heard me ‘talk’ about white mold of tomatoes. The fungus that causes white mold, Sclerotinia sclerotiorum, has a wide host range. Important hosts include bean, cabbage, potato, lettuce and sunflower in addition to tomato. More about the disease on tomato can be found here. If you have never heard me talk about white mold of watermelon, don’t feel left out. I don’t talk about white mold of watermelon since I have only observed the disease twice in 21[Read More…]


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