106 articles tagged "Plant Disease Management".

Many vegetable growers are closing in on the final harvest. Several growers have asked me about fungicide applications late in the season. In this article, I want to address when to stop. To limit the scope of this article, I will concentrate on tomato, cantaloupe and watermelon crops. These are crops where the fruit is consumed, not the foliage. For most vegetable crops, there is no need to apply a fungicide shortly before the final harvest. Foliage needs to be protected to preserve fruit quality. A plant with reduced foliage will produce a smaller fruit and/or fruit that have fewer sugars and other desirable compounds. I don’t know how much foliage needs to be reduced to affect fruit size or quality. However, I do know that for many foliar diseases, symptoms will not be obvious for a week to 10 days. It will take even longer for the foliar disease to significantly reduce foliage. Therefore, for[Read More…]


Figure 1. Powdery mildew on cucumbers grown in a high tunnel.

Powdery mildew is particularly severe in high tunnel and greenhouse growing conditions (Figure 1). It affects a wide range of crops including tomatoes and cucumbers. In addition to using synthetic fungicides to control this disease in high tunnels, we found powdery mildew on cucumbers can also be effectively controlled through variety selection and intensive plant pruning. Cucumber cultivars grown in high tunnels are parthenocarpic. Most of these cultivars are marketed as powdery mildew resistance. However, there are actually a wide range of different levels of resistance existed among parthenocarpic cultivars. In our trials, we found Japanese type cucumbers, especially cultivar Tasty Jade, was very susceptible to powdery mildew; Taurus was less susceptible than Tasty Jade, but much more susceptible compared to most Beit alpha (or mini) type, long English (or Dutch greenhouse) type and American slicer cucumbers. Comparing three long English cultivars in our evaluation, Kalunga was more susceptible compared[Read More…]


Vegetable growers are used to scouting for pests such as spider mites and aphids. Growers have come to recognize the yellow leaves caused by spider mites and the curled leaves caused by aphids. Growers understand that even after spider mites and aphids are dead, the symptoms of the damage may remain on the affected leaves. Whereas, a leaf distorted by aphids remains distorted even after the aphids are dead, a leaf with symptoms of a foliar disease such as anthracnose of watermelon or early blight of tomato typically contains viable spores even after repeated fungicide applications. So, what is the purpose of fungicide applications? Contact fungicide applications with active ingredients such as chlorothalonil (e.g., Bravo®, Echo®, Equus®, Initiate®) or mancozeb (e.g, Dithane®, Manzate®, Roper®, Penncozeb®) are used to coat the surface of the leaf so that when spores land on a leaf, they are neutralized. While it is true that[Read More…]


Anthracnose of garlic, a new disease to Indiana, may cause sunken, orange lesions on scapes.

Earlier this summer, sunken lesions were observed on garlic scapes on a small farm in east central Indiana. Lesions started out a cream or tan color (Figure 1), however under rainy or humid conditions, spore production caused lesions to turn orange (Figure 2). Larger lesions resulted in the collapse of the scapes. It is estimated that 45 to 50 percent of scapes were affected. Lesions ranged from ¼ to ½ inch long. Samples of these scapes were sent to the Purdue Plant and Pest Diagnostic Laboratory in West Lafayette where they were diagnosed as anthracnose of garlic, a new disease to Indiana. This new disease is caused by the fungus Colletotrichum fiorinae. This fungus has also been reported on elephant garlic in New York. Reports from New York suggest that onion is unaffected. In the US, C. fioriniae has also been reported as an Apple post-harvest decay, causing bitter rot on[Read More…]


The 2019 production season started with above-normal rains. The wet conditions affected agriculture production, including watermelon and cantaloupe. In this article, we will review some of the watermelon and cantaloupe problems that are often associated with wet conditions. Manganese toxicity– This nutrient disorder occurs more often on cantaloupe that is grown in soils with pH lower than 5.5. Although liming before planting is a common practice, it is not unusual that we see soil pH that has dropped below 5.5 in sandy soil, especially during wet years. Manganese exists in soil solution as either reduced (Mn2+) or oxidized (Mn3+) form. Plants take up manganese in the reduced form (Mn2+). The proportion of exchangeable Mn2+ increases dramatically as soil pH decreases, and this reaction is promoted in waterlogged soils with low oxygen condition. As raindrops fall through the air, they dissolve CO2 and form enough carbonic acid to lower the pH of[Read More…]


Anthracnose of strawberry causes sunken lesions.

At the Southwest Purdue Ag Center, we are studying annual strawberry production on plastic mulch. Our hope is to gather information on the best methods and varieties to use for annual strawberry production in Indiana. As we learn about insect and disease problems, we will pass this information on to producers. This article is about the diseases we have observed in our strawberries which were planted in March 2019. Strawberry leaf spot-Lesions on leaves start out purple. As the lesions enlarge, the center becomes gray-brown (Figure 1). Under rainy conditions, lesions may coalesce across leaves and cause large necrotic areas. Lesions on stems and petioles may cause dieback. Yield or fruit quality loss can be caused by leaf spot under severe conditions. Although leaf spot symptoms are spread throughout our trial, this disease has not become serious for us. There are several cultural methods of managing leaf spot. Host resistance[Read More…]


Figure 1: Bottom rot of lettuce often causes stunting and wiling.

Although Indiana is not known for lettuce production, an increasing number of growers find that augmenting retail sales with leaf lettuce can be profitable. Since lettuce is a cool season crop, field planted leaf lettuce around Indiana may be reaching harvest stage. Leaf lettuce can generally be grown with few pests. However, lettuce drop was recently observed in a field of mixed lettuce varieties. Lettuce affected with lettuce drop often first appears stunted. A closer inspection may reveal that outer leaves are wilted and necrotic (Figure 1).  Eventually, the entire plant may die. If the plant is removed from the ground and observed, the leaf ribs that touch the ground may exhibit dark, rotten appearing lesions (Figure 2). The lesions may be associated with dark fungal bodies known as sclerotia (Figure 3).  Fortunately, lettuce drop does not often spread from plant to plant. The plants that are diseased will most[Read More…]



Ever year, I put together fungicide schedules for cucurbits. These may be found at purdue.ag/pumpkinfs and purdue.ag/melonfs. They may be downloaded as PDFs on legal sized pages.  Please use these tables along with the MW Vegetable Production Guide and the fungicide label.  If you have trouble with accessing the tables or have other questions. please let me know.


Figure 3: Fusarium wilt symptoms on watermelon transplant.

A recent observation of gummy stem blight on a watermelon transplant has reminded me to remind growers to inspect seedlings. Whether one is growing transplants or receiving transplants for delivery, seedlings should be inspected for possible disease problems. If one is uncertain of the cause of the symptoms, an official diagnosis can be obtained by sending the sample to the Plant and Pest Diagnostic Clinic. Below I will describe several common transplant diseases of cantaloupe and watermelon as well as management options. I have had similar articles in the Hotline in the past, however, I will use new photos here. Gummy stem blight on transplant seedlings may be recognized by the water-soaked area of the stem near the seed leaves. In this article, I will show a leaf with a lesion of gummy stem blight (Figure 1). A closer look (one may need a 10X hand-lens) at any gummy stem[Read More…]


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