Management of Nematodes in Blueberry
In new plantings it is best to avoid nematode problems by submitting a soil/root sample for nematode analysis well in advance of planting and then fumigating or fallowing the ground if necessary. However, keep in mind that we have no data from Oregon as to how good a procedure this would be for a long-lived perennial.
On sites where nematode populations have traditionally been fairly high (the presence of any dagger nematodes or 1,000 or more root-lesion nematodes per quart of soil), nematode populations may not remain low indefinitely after fumigation. By fumigating the soil, one allows young blueberry plants to become well established while nematode numbers are low. Over time, nematode populations may increase to numbers capable of reducing the vigor of a planting.
Symptoms of possible damage from nematodes include poor growth and/or poor leaf color beginning in small patches or areas of the field which expand over the years. If nematode damage is suspected, a sample of soil and roots should be collected from problem areas within the berry row and sent to a laboratory for analysis.
It is usually best to sample weak and healthy areas separately and submit two samples for analysis so that nematode populations in weak and healthy areas can be compared. Confirmation of damaging levels of nematodes is necessary, since symptoms of nematode damage often mimic those of other soil-related problems.
Unfortunately, there is little that can be done to reduce nematode populations once they become high enough to cause problems in an established planting. There are no chemicals available for control of nematodes in an established blueberry planting at the time of the writing of this publication (refer to pest management guides for current information, see (Bibliography).
One possible option may be to remove plants, taking as much of the roots as possible, from infested areas and spot treat with an appropriate soil fumigant prior to replanting. In blueberry plantings without a permanent sod cover where bare soil is exposed, care should be taken to avoid spreading nematodes via equipment or plants moved from weak, infested areas of the field to healthy ones.
However, perhaps the best way to reduce damage from increasing nematode populations during the life of the planting is to maintain optimum plant health. A vigorous plant which is not stressed by other biological, environmental, or cultural factors can tolerate higher nematode populations without damage than a plant that is stressed by other factors as well.
Sampling for Nematodes in Blueberry
Nematode populations fluctuate throughout the year, affecting the number of nematodes recovered at various sampling times. Recent studies in blueberry and raspberry indicate that root-lesion nematode populations peak in July to September and dagger nematode populations peak in February to May. The best time to collect a soil sample is during periods of peak population for the species of greatest concern. If both dagger and root-lesion nematodes are known or suspected to be in an area, sampling in the spring and the fall may be necessary. Samples collected at other times of the year may give readings that are low compared to what the populations will be in summer.
Root-lesion nematodes may be found in both soil and roots; therefore, submission of both soil and root samples is recommended. However, if the ground has been prepared for planting as described under Plantation Establishment Site Preparation, live roots may not be present.
The best way to collect soil samples is with a soil probe. Each probe full of soil constitutes one subsample. Taking several subsamples will result in a more representative and accurate sample. For this reason, collection of at least 20 to 30 subsamples for every 1 to 5 acres is generally recommended. Fields larger than 5 acres should be divided into sections, with separate nematode samples taken from each section. The subsamples should be drawn from sites chosen randomly throughout the field, usually by walking in a “W” pattern, and then mixed together in a clean bucket. Areas with different soil types or cropping histories should be sampled separately.
Preliminary research indicates that only a few nematodes are found in the upper 3 inches of the soil, or in the sawdust mulch. Therefore, it is advisable to insert the soil probe to a depth of 12 to 15 inches and remove the top 3 inches of soil (or sawdust) before putting the subsample into the bucket. Once subsamples have been collected, mix the soil together and fill a quart-size plastic bag.
Roots should be collected with a shovel from several locations in the area to be sampled. Enough roots to fill a quart bag are necessary for an adequate sample. The roots may be added to the bag containing the soil sample or placed in a separate bag with enough soil to keep roots from drying out.
Because high temperatures and drying will kill nematodes in the sample, it is important to keep the sample in a cool, shaded spot or in the refrigerator until it is sent to a laboratory. Samples should be sent for analysis as soon as possible.
Instruction forms and information regarding lab fees and fumigants are available from your local county Extension office.
This fact sheet is adapted from Oregon State University Extension Publication PNW215, Highbush Blueberry Production. The authors of Highbush Blueberry Production are – Oregon State University: Bernadine Strik, Glenn Fisher, John Hart, Russ Ingham, Diane Kaufman, Ross Penhallegon, Jay Pscheidt and Ray William; Washington State University: Charles Brun, M. Ahmedullah, Art Antonelli, Leonard Askham, Peter Bristow, Dyvon Havens, Bill Scheer, and Carl Shanks; University of Idaho: Dan Barney. PNW215, Highbush Blueberry Production can be purchased from the Department of Extension & Experiment Station Communications, Oregon State University. How to Order