Many readers are concerned with bramble appearance at this time of year, and clinic telephone inquiries about brambles have been common as well. The most common diseases that may be involved are anthracnose, cane blight, and spur blight, and we have seen each of these diseases in 1999. All are easy to diagnose with the aid of Reports on Plant Diseases No. 700 and 709.
Although fungicides control the diseases if they are used as preventive sprays, we prefer to stress some cleanup measures that should help considerably. A bramble spray schedule can be found on page 120 of the Illinois Homeowner’s Guide to Pest Management. Horticulture specialist Allan Otterbacher, who manages small fruits on the campus farm, recommends removal and destruction of all fruiting canes as soon as they have finished fruiting. Do not touch the young cane that will bear next year’s fruit. This process decreases the amount of future fungal inoculum, and it opens the planting to better air circulation and more rapid drying. Refer to University of Illinois Circular 1343, Small Fruits in the Home Garden, for information on culture of raspberries.
One other disease that we sometimes see on raspberry- especially Heritage red raspberry--is a root and crown rot caused by Phytophthora. This fungus invades in very wet seasons and on poorly drained sites. The plant loses vigor because roots are rotted and uptake of water and nutrients is inhibited. Infected plants may be stunted; and the rotted roots may have an interior color of brown or red-brown, whereas healthy roots have white inner tissues. Phytophthora may cause the stem to turn brown or black an inch or two above the soil line. Symptoms alone cannot provide a positive diagnosis of Phytophthora root and crown rot, so laboratory confirmation may be necessary. Ridomil has been used in commercial settings to control the disease, but improving soil drainage is also necessary.