28 May 2013

Foliar, Stem, and Vascular Diseases

Leaf spot diseases are known to increase when K is deficient. Similar symptoms appear with Alternaria, Stemphyllium, and Cercospora. These symptoms can sometimes be confused with foliar fertilizer (salt) injury symptoms.

Foliar fertilizer injury can also be confused with other field problems, including leaf spot diseases, and drift from certain herbicides. Spotting can occur when soluble salts accumulate and leaf tissues are damaged. Potential for injury is greatest when foliar fertilizers are applied at high nutrient concentrations to plants that are under

Fusarium wilt can occur at any stage of plant development and is often associated with root-knot nematode injury. Stem (vascular) discoloration is darker than that of Verticillium wilt. A continuous ring of discolored tissue may be apparent in vertical cross section.

Leaf symptoms of Verticillium wilt cover a wide range and can be confused with Fusarium wilt. It may be necessary for a plant pathologist to confirm the disease using microscopic and culture techniques.

Stem symptoms of Verticillium wilt include brown flecks of the lower stalk and dark brown streaks in xylem vessels. Fusarium wilt discoloration of stems is usually darker than with Verticillium and is restricted to the vascular tissue. Vascular discoloration with Verticillium wilt is more evenly distributed throughout the stem.

Bronze wilt symptoms may appear as reddened, wilted, bronzed leaves and reddening of the upper plant stem and branches supporting leaves. This should not be confused with P or K deficiency. No vascular discoloration is evident and shedding of small squares may occur.

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