Using Post-Plant Nematicide Applications for Nematode Suppression

The spray applications with Movento were made on October 19, 2016. Watering scheduled as shown in the overview. On October 28 one of the grape plants was removed. Active leaves, and fibrous roots were excised, and provided after grinding to the Daane laboratory for analysis. Nematode population densities were determined at treatment time (October 18) and post-treatment (January 25). Soil samples were taken from 0-1 and 1-2 ft depth. After extraction, nematodes were identified and counted.

Nematode counts were analyzed before treatments (Fig. 1). Telone II fumigation reduced nematode numbers effectively. At treatment time, nematode numbers were similar among spirotetramat (Movento) treatments although some variability was measured. In parametric analysis, the “watering regiment Movento” treatment combinations analyzed as two-factor factorial design had no significant main effects or interactive effects (data not shown). Soil samples are currently processed to determine nematode numbers post-treatment.

The chemical detection of spirotetramat and its break-down products is initiated. It was possible to detect spirotetramat in the leaf tissues (Fig. 2). No spirotetramat was detected in the plants from the drench-treated plots. There were traces in the Telone-treated plots and in the non-treated controls. These appeared as false positives, and each case was only based on the detection of spirotetramat in one of the five replicate plants of the respective treatments. No spirotetramat was found in roots (data not shown).

The spirotetramat enol was found in leaves and roots from plants of all treatments (Fig. 3, 4). It is currently unclear how this can be explained. We are examining plants of the same source for the potential presence of some of these chemicals before treatment to assess if these could be carrying a back-ground amount of the chemicals. A careful review of our laboratory procedures did not provide any indication of experimental/technical errors that could have led to this find.

Conclusions and outlook

Progress has been made to establish the laboratory method to detect different forms of spirotetramat and its break-down products. A microplot experiment is in place that will be treated in the spring while allowing for additional destructive sampling of chemical analysis and nematode population density monitoring. Population densities of the nematode will provide additional clues on the efficacy of the treatments.

Breeding Rootstocks Resistant to Aggressive Root-knot Nematodes

The USDA Agricultural Research Service grape rootstock improvement program, based at the rape Genetics Research Unit, is breeding rootstocks resistant to aggressive root-knot nematodes. We define aggressive root-knot nematodes as those which feed on and damage the rootstocks Freedom and Harmony. In 2010 we released Matador, Minotaur, and Kingfisher, three root-knot nematode resistant grape rootstocks. We screened 5383 candidate grape rootstock seedlings (representing 45 different populations) for resistance to aggressive root-knot nematodes. We select only those seedlings which completely suppress nematode reproduction and show zero nematode egg masses. Selected seedlings are propagated and then planted into the vineyard. We planted 352 root-knot nematode resistant rootstock selections into the vineyard at the University of California Kearney Research and Extension Center. We screened an additional 25 seedlings exclusively for nematode resistance genetics studies. We tested the propagation ability of 120 selections (already tested once for nematode resistance) and of these retested 33 selections to confirm nematode resistance in replicated trials. We planted 11 selections, grafted to Syrah, into a new rootstock trial at the University of California Kearney Research and Extension Center and provided 11 rootstock selections to Foundation Plant Services for virus disease testing. We pollinated 393 clusters of crosses in 60 unique combinations specifically aimed at the breeding of improved rootstocks with resistance to aggressive root-knot nematodes.

Development, testing, and introduction of Grape Rootstalks with broad and durable nematode resistance

We continue toward our goal of developing grape rootstocks with broad and durable
resistance to nematode species that are important in California vineyards. Few of the
currently available grape rootstocks have resistance to more than one nematode species.
In previous years, we have screened rootstock candidates against the root knot nematode
(Meloidogyne incognita race 3), two strains of root-knot nematode that overcome the
resistance of Harmony rootstock (Meloidogyne arenaria strain A and Meloidogyne
incognita strain C), and the dagger nematode (Xiphinema index). Fourteen rootstock
candidates exhibit broad resistance to those nematodes. This year, we continued to test
the breadth of that resistance beyond the range of the primary screen species by
evaluating the resistance of the 14 candidates to the ring nematode, Mesocriconema
xenoplax. Only one of the rootstock candidates exhibited any resistance to the ring
nematode and we are looking for new sources of resistance. We also continued to test the
durability of nematode resistance of the rootstock candidates when they are exposed to
combinations of nematode species, including species such as the ring nematode for which
they are hosts. We extended and repeated, using greater precision of temperature control,
experiments to determine the durability of resistance at different temperatures.
Resistance of several of the rootstock candidates to several root-knot nematode variants
was compromised at soil temperatures of 30°C and above but appeared durable at 27°C
and below. Resistance to Xiphinema index was not compromised by soil temperature in
any of the rootstock candidates. Field testing of the rootstock candidates continues in
fields that were heavily infested with root-knot nematodes. Nematode population levels
are declining in the root-zones of all rootstock candidates, indicating that reproduction of
the nematode is not occurring.

Breeding rootstocks resistant to aggressive root-knot nematodes

The USDA grape rootstock improvement program, based at the Plant Genetic Resources Unit, is breeding grape rootstocks resistant to aggressive root-knot nematodes. We define aggressive root-knot nematodes as those which feed on and damage the rootstocks Freedom and Harmony. In 2003 we screened 4058 candidate grape rootstock seedlings for resistance to aggressive root-knot nematodes. We select only those seedlings which completely suppress nematode reproduction and show zero nematode egg masses. These selected seedlings are propagated and then planted into the vineyard. We have 81 nematode resistant selections that will be ready for vineyard planting in spring 2004. In 2003 we planted 145 nematode resistant rootstock selections in the vineyard. These selections were identified in nematode resistance screening in 2002 and earlier. In 2003 we pollinated 1287 clusters of crosses specifically aimed at the breeding of improved rootstocks with resistance to aggressive root-knot nematodes.

Xiphinema index and Grape Fanleaf Virus Disease Complex: Defining Nematode

We have initiated experiments using large soil containers (4′ X 5′ X 5′) containing a coarse sand:clay mix. The containers were selected to allow us to simulate field conditions, with controlled soil conditions. The containers were planted in the spring of 1996 with the highly susceptible Rupestris St. George rootstock, to allow nematode (Xiphinema index) populations to increase. The plants were inoculated with Grape Fanleaf Virus (GFLV) with or without X. index during summer of 1996. Our objective is to determine how X. index and GFLV, separately and together, influence nematode population dynamics, virus prevalence, and plant growth and yield relative to rootstock. Upon sampling the units during late summer of 1997, we observed all nematode stages, (juveniles to adults), in all containers save one, indicating nematode reproduction. In addition, we observed nematode feeding damage on the roots, with large terminal galls at root termini. We counted nematode numbers in each experimental treatment, and interestingly, the nematode densities in the nematode and GFLV treatment were significantly lower than where the virus was absent. Although this is preliminary data, it suggests a previously undocumented interaction between the nematode and the virus, and that the presence of the virus reduces nematode reproduction. It is possible that this is due to a general decline in vine vigor due to the combined influence of the nematode and the virus. This research is continuing, and we should be able to ascertain details of the interaction between virus and nematode through more intensive sampling. In late spring of 1998 we move into the next phase of the experiments, and will introduce a resistant rootstock to half of the experimental units, so that we can document the influence of resistance on nematode dynamics, virus transmission and prevalence, and plant growth and yield.

Nematode Evaluation of Eight Rootstocks Present in Existing Field Trials

Selected grape rootstock trials from 5 to 22 years in age were evaluated around California. In these trials mixtures of nematode species had built up giving us an opportunity to validate our previous data from microplot settings. Data from four to five replicates were collected from each site. Many trials had at least 10 rootstocks. A few had only two or three but were older, thus making them worthwhile to sample. We eventually collected samples from 15 sites in Kern County, three in Fresno County, three in Monterey County, one each from Sonoma, Mendocino and Merced counties, and will be sampling one from San Joaquin County. The nematode data from more than 1,100 soil samples are still being analyzed but attached are two charts showing our method for comparing field data with existing microplot data in sites where Xiphinema index was present. This work is tedious and expensive and my concern is that the payoff may not be as great as other studies we hope to conduct in the future. The major problem is that even when rootstock trials are 5 years old and the nematodes are not yet evenly distributed across replicates, resulting in false negatives. Nonfumigated sites such as the field in Mendocino on Chart 2 did not help to clarify. The Mendocino field did not have an own-rooted comparison but we are able to “guesstimate” based on the populations on 3309. There were also advantages to this work. The primary advantage was the opportunity to sample sites with mixed populations where nematodes may be competing with one another or other soil microbes. We have learned that 1103P is too good a host for X. index but remain unclear on 110R and 101-14. Root knot nematode resistance in Freedom and Harmony was nonexistent in two of three older trials in Fresno County, although their tolerance to the nematode and extreme vigor has kept them from declining below the own-rooted. The field-derived data do appear to validate our previous microplot work. VR 039-16 is supporting X. index in one replicate of Kern County and at a separate field site in Monterey. This needs further investigation.

A Broad Nematode Screen to Evaluate Four Potential Nematode Resistant Rootstocks

The USDA-Fresno was able to provide good quantities of each of the 3 rootstocks by April 1992. We also rooted lesser quantities of various USDA numbered hybrids that appeared interesting and screened those alongside. The complete root knot screening is complete as of this writing, and is presented in Table 1 attached. The Ramsey x Schwarzmann cross provided 800 seedlings. They received their first screening in January, 1993 against a moderately aggressive root knot from the Malaga area. We had 116 of these with no galls and zero root knot build-up. In April 1993 the 116 were divided into 36 of low vigor, 35 of moderate vigor, and 44 of high vigor and each screened against our three most aggressive root knot populations. One can see from Table 1 how some of the more interesting rootstocks performed in comparison to industry standards of Ramsey, Freedom, Teleki 5C and Harmony. In the screening process a number of farm advisors provided us with vineyard soil having root knot nematode problems. These mixed populations revealed that although 8-10B performed well against 3 of our most aggressive root knot populations it did not succeed against common field populations of root knot. It also shows the results of a 2 year study involving those rootstocks and Ring nematodes indicating that each has performed at least as well as Harmony. Our data for other ectoparasites will be available in 10 months. Based on the numbers in Table 1 we already have five rootstocks with broader root knot nematode resistance than the best industry standards. These include 10-17A, 10-23B, 6-19B, 3-3A, and possibly 8-17A. Each of these has differing parentage which is an asset when it comes time to make rootstock decisions at the farm level. The 6-19B rootstock roots well but may have some vigor problems. The 3-3A rootstocks is providing good vigor and a healthy-appearing root system. We will need to examine the mode of resistance on this one. This work is well underway and we hope the bulk of it will be completed with only 2 years of funding. In growers’ fields this year we have found at least two new root knot pathotypes which perform similar to but not exactly like the H. arenaria pathotype Harmony. To have a successful rootstock one must be able to protect against all root knot populations present in the field. That is the “lofty” goal of this work.