Consider nematodes when establishing orchards and vineyards
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Many things need to be considered when establishing or replanting an orchard or vineyard, but the impact of plant-parasitic nematodes should not be ignored. Feeding by many species of nematodes will produce unthrifty trees and subsequent yield reductions. Unfortunately, often the cause of these symptoms is undetermined. Since all species of plant-parasitic nematodes are microscopic, the only way to diagnose nematode problems is to collect soil and root samples and to submit them to a nematode diagnostic lab for analyses. It is highly recommended new orchard or vineyard sites are sampled for nematodes before their establishment. Although this article focuses on pome fruits, stone fruits and grapes, the same is true for plantings of brambles, blueberries, strawberries and any other fruit.
The recent withdrawal of fenamiphos (Nemacur) as a post-plant nematicidal option on pome, stone and small fruit magnifies the importance of sampling prior to planting. In the past, if nematodes were abundant on a site at planting but went undetected or nematode-infested planting stock was purchased or used, Nemacur could be used as a rescue treatment and would provide adequate to excellent control of these pathogens. However, with the withdrawal of Nemacur, there are no post-plant chemical options for nematode control in bearing orchards, grapes or small fruit plantings, so most management strategies and tactics must be implemented prior to orchard or vineyard establishment.
If old orchards or vineyards are too be removed and replanted, growers should make observations prior to these events. Are some of the trees stunted and what are the possible causes? Do any of the symptoms appear to be caused by viruses? If the answer to either of these questions is “yes,” nematodes may be implicated as causal agents or vectors. Proper identification of viruses is very important. Dagger and needle nematodes are common parasites of fruit and are notorious vectors of certain plant viruses. Where they are pathogens (cause disease), dagger nematodes, in particular, aren’t extremely virulent (amount of disease). However, only one dagger nematode is necessary to transport viruses from one tree to another. Therefore, if old orchards or vineyards are infected with nepoviruses (nematode-transmitted polyhedral viruses), dagger and needle nematode control is vital before establishing new plantings. Many broadleafed weeds are also symptomless carriers of some nepoviruses, so observations about weed pressure are also important.
Typically, after removal of an old orchard or vineyard, some remediation of the site will occur before replanting. This is typically done by growing cover or rotational crops or even allowing sites to sit idle. These periods represent good windows for nematode control. However, it is virtually impossible to develop a sound rotational scheme or to choose the proper cover crops if the types of plant-parasitic nematodes present are not determined. For example, rape, cv. Dwarf Essex, is a great choice if dagger nematodes are present on a site, but it may not be real effective against lesion and northern root-knot nematodes. Pearl millet should be very effective against lesion nematodes but possibly poor against dagger nematodes. Therefore, the collection of soil and root samples is necessary for identification and enumeration of important nematodes present in any given location in order to design rotational schemes to reduce their population densities.
Maintaining good soil health is very important for proper nutrition and growth of plants. With orchards and vineyards, it is very critical to check soil pH deep in the soil prior to establishment because, on occasion, soils in the rooting zones of trees and vines are very acidic. At low pHs, heavy metals are much more mobile and in concert with other causal agents, such as nematodes, growth can be significantly reduced. In these types of situations, young trees may even die.
All your diligent work to avoid nematode problems prior to planting can be wasted if nematode-infested planting stock is used. Virus certification programs often work well to reduce or eliminate the sale of trees or plants infected with viruses, but nematodes often go unchecked. If sites are fumigated prior to planting nematode-infested stock, severe problems may result as nematode population densities can increase dramatically if unchecked by biocontrol agents or competing organisms.
Management of plant-parasitic nematode populations requires an integrated approach. However, it all begins with a sampling program. Once nematodes are properly identified informed decisions can be made regarding fumigation, cover crops, resistant rootstocks, etc. In Michigan, nematode samples can be sent to the MSU Diagnostic Services on campus. The fee is $25 for a standard nematode analysis where all genera of plant-parasitic nematodes are identified and counted. Results typically will be available in seven to 14 days. Questions or concerns about nematodes can be addressed to Fred Warner at (517-432-1333) or Angela Tenney (517-353-8653) in Diagnostic Services or Dr. George Bird (517-353-3890) in the Entomology Department.