Alternatives and Improvements to Soil Fumigation with Methyl Bromide

We have now reached the point where certain treatments are ready for field evaluation in certain field settings. Our research is now taking two directions. First, we need to continue small plot evaluations in our search for additional root killing agents of any kind. Second, we need to conduct field evaluations of combinations of the successful treatments listed above. These include:

  1. Use of Telone and Vapam drench through existing mirco sprinklers or drippers where resistant stocks are to be used or nematodes are not present.
  2. Use of Vapam at 100 to 150 gallons/acre where ectoparasites are the problem.
  3. Use of Urea drench followed by sudan grass where root kill has been accomplished by some other means. We are ready to do this in walnuts.
  4. Use of high rates of Vapam then waiting one year.
  5. Use of Garlon plus diesel painted to cut trunks in late summer after harvest.

Improvements and Replacements for Pre-Plant Soil Fumigation

Garlon at 5 and 10 grams active ingredient applied to foliage or applied as a paint to stumps was highly effective at killing the surface 1 foot of grape roots and all aboveground portions. It was ineffective, however, at killing roots below 1 foot soil depth. Certain grape rootstocks are more sensitive to the replant problem than others. Teleki 5C is among the more sensitive, whereas own-rooted V. vinifera appears less sensitive. We now have good evidence that Vapam at 100 gpa is a mediocre performer relative to killing old roots and that treatments with Vapam, like methyl bromide or Telone, result in a biological vacuum. By broadcast drenching at 200 gpa and then growing nonhosts for the nematodes in the next year we have in one large trial achieved nematode control and vine growth comparable to that achieved with methyl bromide. We now need to adjust the treatment rates lower to find the best rates for use in vineyards as compared to orchards. Telone or Acrolein applied via a drencher at rates equivalent to 100 gal/acre Vapam will outperform Vapam. Applied via drencher Telone volatilization can be reduced from that which occurs after conventional shank injections.

Improvements and Replacements for Pre-Plant Soil Fumigation

High-pressure steam, hot air, hot water, and two years of solarization are ineffective fumigation replacements because heat cannot be distributed adequately through soil. Deeper placement and lower treatment rates with MB can deliver effective nematode control while reducing somewhat the MB volatilization, but control of weed seeds will be lost. Our soil drenching experiments show greatest potential as a replacement. Soil pest control and kill of old peach roots is equivalent to that attained with Telone or MB when 200 gal/ac Vapam is used. However, plant growth following 200 gal/ac does not keep pace with that of MB, Telone, or 100 gal/ac Vapam. One immediate spin-off from the drenching work is that growers already having drippers or planning to install them prior to replanting can use our drenching recipes today. Evaluation of the use of Roundup prior to tree and vine removal indicates that for Nemaguard rootstock the treatment can work well but not for plum roots. Our grape work involves Garlon, 2, 4-D, and Roundup. Rotation crops may have some value if complimentary methods of root kill become usable. Forty days and nights of flooding will not kill nematodes or old roots oiPrunus. Cabernet Sauvignon on Teleki 5C does not grow as well in a replant site as Cabernet on its own roots. It also did not respond as well to the Vapam drench (first year).

Influence of Potassium Deficiency and Temporary

Executive Summary The aim of the proposed research was to study several sites with a history of potassium deficiency using a rapid screening procedure for putrescine levels that we developed in previous work on this project. The objective was to validate our screening procedure and provide recommendations regarding sampling time so that putrescine screening can be used routinely for managing potassium deficient vineyards. During the 1992 season we analyzed leaf samples for putrescine by HPLC and a recently developed TLC screening procedure that increased sample throughput by an order of magnitude. Results show that our screening procedure can certainly be used for Cabernet sauvignon and Chardonnay and can probably be used with other varieties. The screening procedure can be used to detect elevated putrescine in leaves at bloom whether or not leaf symptoms are present. The screening procedure is equally useful at veraison and after harvest. In all cases when samples were scored by TLC as having increased putrescine, the result was confirmed by HPLC. False positives and false negatives were not observed. Putrescine in leaves as estimated by the screening procedure correlated well with a subjective evaluation of the degree of potassium deficiency suffered by the vine. Results obtained during the 92/93 season served to validate of our screening procedure. We can now provide specific recommendations regarding sampling time so that putrescine screening can be effectively used for managing potassium deficient sites. In addition we have identified several “ideal” locations to apply the procedures we have developed. Interestingly, we found one site in our study that did not fit the typical potassium deficiency syndrome. This site provides an opportunity to characterize other disorders besides potassium deficiency that can lead to increased putrescine levels in the leaves.