What Is Wrong With My Rapeseed Field?

Are there any small dark spots on leaves which turn brown to gray, lesions may be round or angular and may possess a purple-black margin?

Are there any irregularly shaped dull yellow areas along leaf margins which expand to leaf midrib and create a characteristic "V-shaped" lesion?

Do the leaves have pale areas on upper surfaces and "downy" patches underneath?

Are the stems bleached, there is a white fungal growth on the stems near the soil line, black fungal structures develop in the white fungal mass?

Are there any white masses of fungal spores on the underside of leaves, green blisters on the leaves which turn white?

Are there any circular gray lesions on the leaf surfaces with black specks forming in the center?

Are the leaves distorted and yellow, clusters of small insects are present?

These symptoms indicate Alternaria leaf spot. Warm, wet conditions favor this fungal disease. Spray infected plants with copper and/or sulfur to prevent further disease development.

These symptoms indicate a bacterial disease - Black rot. Prevent this disease by providing well-drained soil and by using a 2-year rotation. Plant resistant varieties. Control cruciferous weed species which may act as a reservoir for bacteria. Plant pathogen-free seed.

Pale areas on upper surfaces of the leaves and "downy" patches underneath are caused by Downy mildew. This fungus spreads quickly during cool, wet nights and warm, humid days. Leaves will wilt and die. Remove and destroy all affected plant parts and encourage good air circulation around plants by thining them. Water plants early in the morning to make sure they dry before nightfall.

Sclerotinia stem rot (white mold) is a fungal disease that causes these symptoms. Wet weather conditions favor this disease. The disease is usually introduced to non-infected areas by infected seed. Plant only certified seed. If the disease is known to present rotate crops with non-hosts such as cereals.

Fungal disease White rust causes these symptoms. Disease development is favored by cool weather and periods of extended rainfall. Destroy infected leaves or plants. Remove weeds and any debris from around plants. Avoid the use of sprinklers for irrigation. Apply appropriate fungicide if the disease becomes a problem.

Blackleg is a disease favored by wet weather. The use of resistant varieties is very important in the control of the disease. Rapeseed should be planted on a 3-year rotation to promote plant vigor and reduce disease susceptibility.

Distorted, yellow leaves are caused by aphids. These tiny insects cluster under leaves and on growing tips where they feed on plant sap. Leaves, stems, and buds get distorted, and later leaves and flowers drop from the plant. You can control them by washing them off the plant with water spray. Insecticidal soap should be used with severe infestations.

If there are tiny holes in leaves they are caused by Flea beetles. These tiny, black, brown, or bronze beetles hop when disturbed. Larvae are small and white, feed mostly on the undersides of leaves. Prevent problems by covering young plants with row cover. Control severe infestations by spraying or dusting plants with pyrethrin.