Plant Disease Phenotype

On tomato, leaf lesions are initially circular and water-soaked and may be surrounded by a faint yellow halo. In general, spots are dark brown to black and circular on leaves and stems. Spots rarely develop to more than 3 mm in diameter. Lesions can coalesce causing a blighted appearance of leaves and a general yellowing may occur on leaves with multiple lesions. Infected pepper leaves drop prematurely; this exposes fruit to the sun and results in sun scalding. Fruit lesions begin as small, slightly raised blisters, which become dark brown, scab-like, and can appear slightly raised as they increase in size. On leaflets, bacterial spot can be easily confused with the early symptoms of bacterial speck, early blight, gray leaf spot, target spot, or Septoria leaf spot. When Xanthomonas is present, bacteria will ooze (also referred to as bacterial streaming) from infected tissue and can be observed under a light microscope. Bacterial streaming will not be observed in lesions caused by funga...

Leaf scorch is caused by the fungus Diplocarpon earliana. Symptoms of leaf scorch consist of numerous small, irregular, purplish spots or “blotches” that develop on the upper surface of leaves. The centers of the blotches become brownish. Blotches may coalesce until they nearly cover the leaflet, which then appears purplish to reddish to brown. The fungus overwinters on infected leaves. The fungus produces spore forming structures in the spring on both surfaces of dead leaves. These structures produce spores abundantly in midsummer. In the presence of free water, these spores can germinate and infect the plant within 24 hours. Older and middle-aged leaves are infected more easily than young ones. Scorched strawberry leaves are caused by a fungal infection which affects the foliage of strawberry plantings. The fungus responsible is called Diplocarpon earliana. Strawberries with leaf scorch may first show signs of issue with the development of small purplish blemishes that occur on the t...

  Powdery mildew, mainly caused by the fungus Podosphaera xanthii, infects all cucurbits, including muskmelons, squash, cucumbers, gourds, watermelons and pumpkins. In severe cases, powdery mildew can cause premature death of leaves, and reduce yield and fruit quality. Causes Powdery mildew infections favor humid conditions with temperatures around 68-81° F. In warm, dry conditions, new spores form and easily spread the disease. Symptoms of powdery mildew first appear mid to late summer in Minnesota.  The older leaves are more susceptible and powdery mildew will infect them first. Wind blows spores produced in leaf spots to infect other leaves. Under favorable conditions, powdery mildew can spread very rapidly, often covering all of the leaves. Although powdery mildew primarily infects leaves and vines, infections occasionally occur on cucumber or melon fruit. Powdery mildew does not directly infect squash fruit. Fewer and smaller fruit grow on infected plants. Reduced fruit q...

Found on tomato and potato plants, late blight is caused by the fungus Phytophthora infestans and is common throughout the United States. True to its name, the disease occurs later in the growing season with symptoms often not appearing until after blossom. Late blight first appears on the lower, older leaves as water-soaked, gray-green spots. As the disease matures, these spots darken and a white fungal growth forms on the undersides. Eventually the entire plant will become infected. Crops can be severely damaged Unlike other fungal diseases, this plant problem does not overwinter in the soil or on garden trash. Instead the spores are introduced by infected tubers, transplants or seeds. Wind will also carry the disease from nearby gardens. Warm temperatures (70-80˚F) and wet, humid conditions promote its rapid spread. Note: Late Blight was responsible for the Irish potato famine (1845-1849).  Treatment Destroy all cull and volunteer potatoes. Plant late blight-free seed tubers. Do...

  Early blight of potato is a common disease found in most potato growing regions. The disease is caused by the fungus Alternaria solani, which can also afflict tomatoes and other members of the potato family. Potatoes become infected with early blight when foliage has become excessively wet due to rain, fog, dew, or irrigation. Although not a terminal disease, severe infections can be fairly detrimental. In contrast to its name, early blight rarely develops early; it actually usually affects mature foliage rather than young, tender leaves. Symptoms Early blight rarely affects young plants. Symptoms first occur on the lower or oldest leaves of the plant. Dark, brown spots appear on this older foliage and, as the disease progresses, enlarge, taking on an angular shape. These lesions often look like a target and, in fact, the disease is sometimes referred to as target spot. As the spots enlarge, they may cause the entire leaf to yellow and die, but remain on the plant. Dark brown to ...

Leaf spots that appear on the lower surface of older leaves as small, pimples and on the upper leaf surface as small water-soaked spots are a symptom of bacterial spot. This is an important pepper disease in Maryland. It also occasionally attacks tomatoes. Eventually, the spots develop gray to tan centers with darker borders. Lesions enlarge during warm, humid weather. Leaves may then turn yellow, then brown and drop. Lesions may also develop on stems. Fruits develop small, raised rough spots that do not affect eating quality. Severely infected leaves will drop resulting in sun-scald of peppers. Bacterial leaf spot is spread by splashing rain and working with wet, infected plants. This disease can defoliate plants during wet weather. Hot, dry weather slows the spread of this disease. The disease can come in on seed or transplants and can overwinter in crop residue and soil. Management You can minimize problems with bacterial spot by following these tips: Select resistant varieties Purc...

Bacterial leaf spot of peach, also known as bacterial shot hole, is a common disease on older peach trees and nectarines. This peach tree leaf spot disease is caused by the bacterium Xanthomonas campestris pv. pruni. Bacterial spot on peach trees results in loss of fruit and the overall malaise of trees caused by recurrent defoliation. Also, these weakened trees are more susceptible to winter injury. The most characteristic sign of peach tree leaf spot are angular purple to purple-brown spots on foliage, followed by the center of lesion falling out, giving the leaves a “shot hole” appearance. Leaves soon turn yellow and drop. Fruit has small water-soaked markings that enlarge and merge to eventually cover large areas. Cracking or pitting occurs along the lesions as the fruit grows, enabling brown rot fungus to infiltrate the fruit. Bacterial leaf spot also affects current season growth. Two types of cankers can be spotted on twigs. “Summer cankers” appear on green twigs after leaf spot...