Squash Powdery Mildew

 



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 quality occurs due to increased sunscald, incomplete ripening, poor storability and poor flavor.
  • Powdery mildew is more likely to infect densely planted vines, plants crowded by weeds, plants in shaded sites and over-fertilized plants


Management

  • Plant varieties with complete or partial resistance to powdery mildew.
  • Apply fertilizer based on soil test results. Avoid over-applying nitrogen.
  • Provide good air movement around plants through proper spacing, staking of plants and weed control.
  • Once a week, examine five mature leaves for powdery mildew infection. In large plantings, repeat at 10 different locations in the field.
  • If susceptible varieties are growing in an area where powdery mildew has resulted in yield loss in the past, fungicide may be necessary.
  • Apply fungicides after finding the first spot of powdery mildew.
  • Home gardeners can apply sulfur products to both the upper and lower surface of the leaves.
  • Commercial growers should refer to the Midwest Vegetable Production Guide for pesticide recommendations.



Comments

Post a Comment

Popular posts from this blog

Corn Northern Leaf Blight

Image
  Northern corn leaf blight (NCLB) is caused by the fungus Setosphaeria turcica. Symptoms usually appear first on the lower leaves. Leaf lesions are long (1 to 6 inches) and elliptical, gray-green at first but then turn pale gray or tan. Under moist conditions, dark gray spores are produced, usually on the lower leaf surface, which give lesions a "dirty" gray appearance. Entire leaves on severely blighted plants can die, so individual lesions are not visible. Lesions may occur on the outer husk of ears, but the kernels are not infected. On hybrids that contain an Ht gene for resistance to the fungus, lesions are smaller, chlorotic, and may develop into linear streaks. These lesions rarely produce spores. Lesions can eventually expand to a more oblong or “cigar” shape. They may also coalesce to form large areas of necrotic tissue. Dark spores may be observed in the lesions with the aid of a hand lens. Symptoms often begin on lower leaves; spores produced by primary lesions are
Read more

Tomato Yellow Leaf Curl Virus

Image
Tomato yellow leaf curl is a disease of tomato caused by Tomato yellow leaf curl virus. In March 2007, it was identified for the first time in California and currently has a limited distribution.  Infected tomato plants initially show stunted and erect or upright plant growth; plants infected at an early stage of growth will show severe stunting. However, the most diagnostic symptoms are those in leaves. Leaves of infected plants are small and curl upward; and show strong crumpling and interveinal and marginal yellowing. The internodes of infected plants become shortened and, together with the stunted growth, plants often take on a bushy appearance, which is sometimes referred to as 'bonsai' or broccoli'-like growth. Flowers formed on infected plants commonly do not develop and fall off (abscise). Fruit production is dramatically reduced, particularly when plants are infected at an early age, and it is not uncommon for losses of 100% to be experienced in fields with heavily
Read more