78 articles tagged "Plant Disease Management".

Last fall, my lab received a carrot sample with disease-like lesions (Figures 1 and 2). There are at least 3 carrot diseases that may appear similar. These diseases are: Alternaria leaf blight (late blight), Cercospora leaf spot (early blight) and bacterial leaf blight. Often an examination in the laboratory is necessary. My examination revealed the characteristic spores (conidia) of Alternaria dauci, causal agent of Alternaria leaf blight. Figure 1  shows a stand of carrots with several leaves that appear chlorotic (yellow) and necrotic. A closer examination reveals small lesions on the leaves (Figure 2). Loss of leaves may lead to fewer or smaller carrots. Sometimes severe infections can lead to the premature separating of the leaves and root. Alternaria leaf blight can be rapidly spread between plants by the conidia that are produced on the plant surface. I could easily find these spores on the surface of the carrot leaves brought to my lab. The conidia may[Read More…]

As Indiana growers finish up the 2017 season, it is important to remember to clean and sanitize equipment and tools. In this article, I would like to discuss the importance of and how to sanitize. Bacteria and fungi that cause plant disease may survive on some types of equipment. Examples include: stakes, transplant trays, shovels, greenhouse benches etc. Equipment can be contaminated by diseased plants in close contact with the surfaces. For example, a tomato with bacterial canker may rub up against a wooden stake, transferring some of the bacteria to the stake. Such bacteria may cause disease problems next year. A transplant tray of cantaloupe with a damping-off problem may have the same disease next year if the tray is not properly cleaned and sanitized. It is important to clean the equipment of crop debris or soil prior to the use of one of the sanitizers described below. Equipment free of crop[Read More…]

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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