75 articles tagged "Plant Disease Management".

Figure 3: Mottling of a tomato leaf caused by tomato spotted wilt virus.

Tomato spotted wilt virus can cause stunting (Figure 1), necrotic ring spots (Figure 2), mottling (Figure 3) or chlorosis (Figure 4). In Figure 5, a pepper plant is shown with a ring-like lesion due to tomato spotted wilt virus. Figure 6 is a photo of a pepper transplant with mottled lesions due to impatiens necrotic spot virus. Both TSWV and INSV can cause symptoms on many hosts including ornamentals. Figure 7 is a photo of INSV symptoms on begonia. For more information about the biology and management of these diseases see here.


Figure 2. Media and roots properly secured for shipment

Samples in plug trays, as well as unrooted and rooted cuttings, and plants in pots require extra care when they are packaged for submittal to a diagnostic lab. Before you mail the next sample, please take a few minutes to review these suggestions for packaging and submitting samples. This will help preserve the integrity of the sample during shipment and increasing the likelihood of a more accurate diagnosis. Plugs – keep them in the tray If possible, do not remove the plugs from the plug tray. Submitting either an entire tray or cutting off a section of the tray helps keep the soil off the foliage where most symptoms are observed (Figure 1). Secondary decay often occurs when soil is allowed to come in contact with the foliage, interfering with accurate diagnosis. When possible, submit at least 5-10 cells with plugs. This provides the diagnostician with ample material for microscopic[Read More…]


A tomato leaf with necrotic rings caused by tomato spotted wilt virus.

While many virus diseases affect pepper and tomato plants, in the Midwest, the most common virus diseases of these two crops are tomato spotted wilt virus (TSWV) and Impatiens necrotic spot virus (INVV).  These diseases are usually observed in greenhouse or high tunnel situations. The two viruses, TSWV and INSV are closely related. In fact, at one time, they were both considered TSWV. Therefore, the symptoms, biology and management of these two diseases are similar. This article discusses the symptoms, biology and management of these two diseases. Both TSWV and INSV affect many hosts, including vegetables and flowering ornamentals. Symptoms vary according to host, stage of plant affected and environmental conditions. Both diseases can cause stunting, yellowing, necrotic rings, leaf mottle and more. Figure 1 shows a tomato leaf with necrotic rings caused by TSWV. Figure 2 shows a pepper transplant with ring spots caused by INSV. Additional symptoms may[Read More…]


: These lesions of bacterial speck of tomato were observed on a tomato transplant for sale to homeowners at a retail outlet. Tomato transplants should be inspected for disease symptoms during production or at delivery.

Many Indiana growers may have tomato transplants growing in a greenhouse for field or greenhouse/high tunnel production. The three most likely diseases are bacterial spot, bacterial speck and bacterial canker. This article describes symptoms for these diseases and some management options. While these bacterial diseases thrive in transplant production where plants are often overhead watered, these diseases are not common on tomatoes grown to maturity in greenhouses or high tunnels. This is because, for the most part, tomatoes grown to maturity in a greenhouse or high tunnel do not have the necessary leaf wetness required for these diseases. Bacterial canker is occasionally observed in greenhouse/high tunnel situations since this disease may become established in transplants and becomes systemic in plants. Once bacterial canker is systemic in the plant, it ‘spreads’ within each plant even if it does not spread from plant to plant. Bacterial speck and spot – The symptoms produced by these two diseases are[Read More…]


Figure 1. Lettuce in high tunnel showing symptoms of lettuce drop caused by the fungus Sclerotinia sclerotiurum. Photo by Erin Bluhm.

Some of the red and green multi-leaf lettuce plants in Figure 1 are wilted and closer inspection reveals death and soft decay at the crown and well as freeze damage (Figure 2). Getting even closer as in Figure 3 we see white fuzzy mold and find hard black sclerotia 1/8 to ¼ inch across and up to ½ inch long at the base of the plants and in the soil. These sclerotia confirm that the plants have succumbed to white mold or lettuce drop caused by the fungus Sclerotinia sclerotiorum. The lettuce was transplanted in September or October 2016 and the photos taken in mid to late January. We continue to see more plants succumbing to the disease. Infection by this fungus begins when sclerotia buried in the soil produce small mushroom-like apothecia and spores from the apothecia land on susceptible plant tissue, germinate, and invade the plant. Sclerotia can[Read More…]


Figure 2: We often observe Fusarium wilt in transplant trays in a clustered distribution. We believe that Fusarium wilt may spread from plant-to-plant within a transplant tray, perhaps by soil splash or spores that have been observed on diseased seedlings.

Fusarium wilt is one of the most serious diseases of watermelon in the Midwest. The disease often causes a one-sided wilt 2-3 weeks after transplanting. Whether a plant is affected, and to what degree, depends on the population of the long-lived spores in the soil that the roots contact. However, Fusarium wilt of watermelon is not known to spread from plant to plant in the field. This is in contrast with a disease such as anthracnose which can spread from plant-to-plant rapidly in one season. Occasionally, Fusarium wilt can be observed affecting commercially produced watermelon transplants in new trays and virgin soilless mix. The most likely explanation for such outbreaks is the introduction of Fusarium wilt on seed. The distribution of Fusarium wilt from seed should appear random. However, we often observe a clustered distribution of affected seedlings as seen in Figure 1. We conducted an investigation to determine whether[Read More…]


This backpack sprayer has three nozzles on a boom and a hand-pump that can be worked constantly.

The use of tractor drawn pesticide sprayers is not practical for many smaller growers. Two alternatives are garden-sprayers or backpack sprayers. I will argue here that garden-sprayers are not suited for most commercial pesticide use. The typical garden sprayer that may be found at a garden shop or hardware store usually has a 1 or 2-gallon capacity and a nozzle whose output may be manually adjusted from stream to spray (Figure 1).  Such sprayers use air pressure generated by a hand pump. Some models have a valve to quick-release air pressure. While such sprayers may be useful for cleaning tasks, they are not appropriate for commercial pesticide applications for the reasons stated below. Let’s start off discussing the adjustable nozzles on garden sprayers. These nozzles may be inadvertently moved to provide a different stream or spray. That is, the output may be changed from a full spray to a more[Read More…]


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…]


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