Fact Sheets And Publications
Selecting Plant Disease Specimens
- Select material showing the symptoms you see. Send several samples showing different stages of disease development. Take samples showing transition areas between healthy and diseased. Dead plants, leaves or branches are generally of little use.
- When possible send entire plants including roots. Above ground symptoms may indicate root or stem disease. If not practical to send entire plant, include affected portions of stems and roots. Enclose the soil ball around the roots in a plastic bag and tie securely around the stem. This avoids drying of sample, and having the soil spill on top portions of the plant during transit and cover symptoms on the stems or leaves. Wrap the entire specimen in another plastic bag.
- When entire plants cannot be sent or when only parts of plants are diseased as with leaf spots, dieback, or stem cankers, send several affected pieces. Cut stem and branch specimens with a short piece of live healthy tissue attached to the diseased portion. Place specimens in a plastic bag. Fresh leaf samples keep very well in closed plastic bags. Do not add water or wet paper towels unless the sample is very dry. Keep refrigerated until sample can be sent.
- Dutch elm disease or Verticillium wilt. If you suspect either of these diseases, select branches having wilted, yellow, or dying leaves, not completely dead. Cut and send several branch sections 1/2 to 1 inch in diameter and about 6 inches long. Wrap samples in plastic to prevent drying.
- Turfgrass. Send two or three 3" x 3" squares, containing at least an inch of attached soil, from the edges of areas that include affected and healthy plants. Wrap each sample in a slightly dampened paper towel, then in dry newspaper, or place in plastic container with lid. Turfgrass diseases are sometimes very difficult to diagnose accurately, so include as much information about the problem as possible. Photographs of the lawn are also very helpful.
- Fleshy fruits and vegetables. Select firm specimens showing early and intermediate stages of the problem. Wrap each specimen separately in dry paper towels. Pack individually to avoid crushing and then place entire sample in a plastic bag.
- Pine Wilt Nematode. Cut sections of dying or dead branches up to 5" in length and greater than 1.5" in diameter, close to the main trunk, or take wedges cut from the trunk of dying trees. Sample several branches due to random distribution of the nematodes in the tree. The nematode is present in the trunk and symptomatic branches, not in soil around roots. Place samples in plastic bags.
Samples must be accompanied by a sample submission form available at any DE Cooperative Extension Office. Information requested on the forms is important for diagnosis and may delay diagnosis if not completed. Deliver specimens to Delaware Cooperative Extension Offices in Georgetown (856-7303), Dover (730-4000), or Newark (831-2506). Please try to send samples early in the week so they don’t sit in a mailbox over the weekend.
Nancy F. Gregory, Plant Diagnostician Revision Date: 10/9/2015
Disclaimer: Reference to commercial products or trade names does not imply endorsement by University of Delaware Cooperative Extension or bias against those not mentioned.
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