Consider Fumigating For Nematodes Before Replanting Almonds, Stone Fruit
May 26, 2016 Stone fruit and almond growers looking to replant orchards might want to invest in soil samples to assess nematode populations and the need to fumigate, according to a leading nematode expert.
Andreas Westphal, a University of California, Riverside Assistant Cooperative Extension Specialist, says nematode pressure can significantly affect growth and yield in replanted orchards. Even when tests detect few nematodes, the pests are likely to increase in population in the first few years of a new planting.
“Great care needs to be taken when collecting a meaningful soil sample from sufficient number of spots within a given field. This sample needs to be protected from heating, drying or other extreme handling conditions to preserve the potentially present nematodes,” Westphal says.
Care in the sampling approach is especially needed if the field has been fallow for an extended period; in such cases nematode populations may be temporarily smaller and distributed more deeply in soil than would be the case in a standing orchard.
Westphal suggests a thorough sampling of about eight to 10 cores per acre down to 2 feet deep. If fields are highly variable different strata should be sampled separately.
“Depending on how long your field has been fallow, you want to consider different depths,” he says. “If it has been fallow a long time, your nematode numbers may be low in shallow soil and you don’t get an accurate measurement.”
The most likely nematodes to be found are root knot, root lesion, and ring, and since these pests feed on roots, testing should focus on areas that were former well-rooted soil volumes, most likely near irrigation spots. This becomes more important as drip irrigated or micro-fan irrigation become common.
Westphal says checking with neighboring orchards to see the types of nematodes they have encountered and whether or not they fumigated soil can be helpful. Understanding which species may be present is also important because different soil sampling methods are better at capturing some nematodes and not others.
Pre-plant options are somewhat limited. After the phase-out of methyl bromide, few fumigant options are available. If a grower believes nematodes are a likely issue, 1,3-Dichloropropene (1,3-D)-containing materials such as Telone II (Dow AgroSciences), may be used.
The use of 1,3-D is restricted under a so-called township cap, meaning only a certain amount of material may be used per township and year. If other local growers have used 1,3-D recently, it’s possible that township cap on the chemical could keep others from using it.
Finally, Westphal says to be conscious of rootstocks. Nemaguard is a widely used choice because of its resistance to root knot nematodes, but it is susceptible to root lesion nematodes and ring nematodes. Careful consideration should be given to the type of nematodes present and which rootstock will be best, as well as which will pair well with scions.
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