WALNUTRESEARCHRESULTSFOR1986 STUDYOF WALNUTREPLANTPROBLEMANDEFFICACIOUS METHODSOF CONTROL

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1 ABSTRACT WALNUTRESEARCHRESULTSFOR986 STUDYOF WALNUTREPLANTPROBLEMANDEFFCACOUS METHODSOF CONTROL Michael McKenry The walnut replant problem is primarily a problem with the root lesion nematode Pratylenchus vulnus and secondarily a problem with old roots and rhizosphere organisms. Solid treatments of soil fumigant a~e needed to avoid the replant problem and such treatments can provide up to 6 years of nematode relief. Although soil fumigation provides uniform tree growth it also results in relatively mediocre tree growth. Additions of soil from old peach, walnut or bare soil to the tree sites at planting time can increase tree growth by at least 5% over uninocuated trees. Waiting! years between fumigation and planting does not help in this matter. Root lesion is a major problem because walnut is a good host for all 3 rootstocks tested. Root knot nematode can survive on young walnut roots but does not occur readily on established trees. n the presence of root lesion nematode Paradox will grow more top growth than Eureka or N.C. Black Walnut, however we were unable to identify if it has a degree of tolerance to root lesion nematode. Post plant treatments of fenamiphos (Nemacur) provide reductions in root lesion nematode but not of ring nematode. The root lesion treatments did not appear to improve plant vigor. OBECTVE Phase. Two year field study of the efficacy of various soil treatments in a walnut replant. Phase 2. Demonstrate the value of proper soil preparation prior to fumigation in appropriate field situations statewide. Phase 3. Separation of componentsof Walnut Replant Problem in a "clean" soil including a) walnut root b) root lesion nematodec) rhizosphere soil minus nematodesand roots d) replant soil and e) leachate of walnut root periodically added. Additional Objective Phase 4. dentify if these are special application procedure~ for the successful use of fenamiphos (Nemacur) nematicide relative to established, deep rooted plants such as walnut. PROCEDURES Phase. A walnut replant site at Kearney Ag Center was used for this study. Twelve separate treatments were compared for two years. 86

2 Phase 2. At a Modesto orchard we are comparing the addition of various additives to twentyfour back hoed sites. Additives include:. Methyl 2. Methyl 3. Methyl 4. Methyl bromide + K43 soil. bromide + Verticiium chamydosporium. bromide only. bromide + K43 soil + y. chamydosporium. These treatments are an effort to give longer term biological protection from nematodes at the site once the trees are planted. n several other sites farm advisors have added K43 soil from Kearney to back hoed sites in an effort to fill the biological vacuum created by the preplant fumigation. Phase 3. A walnut replant site at Kearney Ag Center was fumigated in 983 and in 985 a series of 22 separate treatments were compared. Treatments included various components of the replant problem. n 985 Black Walnut, Eureka seedlings and Paradox hybrid were planted with trees per rep and reps per treatment. n 985 and 986 total plant growth was measured and nematode counts were collected from each replicate. n winter 985 the trees were cut to ground level and the 986 regrowth data reflects the root systems ability to re establish top growth. Phase 4 Post plant control n reviewing nematode control work in walnuts since 97 no researcher has identified benefits from nematicide treatments. We decided to test some very different approaches to delivery of fenamiphos nematicide. We compared: ) fenamiphos applied through a sprinkler several times a year 2) fenamiphos mixed with DMSOcarrier painted onto the tree trunks several times a year and 3) installation of ten, foot lengths of dripper tube in a circle around each tree. This tubing with emitters at foot increments was hydraulically placed down to the eight foot depth at a 3 angle away from the tree trunk. The tubes were tied together and used to deliver fenamiphos solutions alongside the presumed coneshaped root distribution of the walnut trees several times each year. RESULTS Phase. Results reported in 985 report to Walnut Board. Phase 2. At the Modesto trial the poorest trees appear to be where Verticillium chamydosporium was added to the K43 soil. t is premature to judge ditierences in this first year. We do not yet have trunk diameter comparisons from other field sites where K43 soil was added in 986. Phase 3. This has been our major effort in 986 and two years of tree growth have now been collected. Even with trees per replicate and replicates of each treatment and 2 years of tree growth data added together we are unable to give very many significant separations among the data. Put another way, we did not have success in our establishment of similar replicates. We suspect this to be inherent in work with the replant problem, but not necessarily the root lesion component of the replant problem since we did get significant effects where root lesion was involved (see Figure and 2). n figure 3 we 87

3 . compare tree growth in the presence of root lesion nematode using 3 different rootstocks. Paradox grows better in the presence of root lesion than either Black or Eureka seedlings. Phase 4. Two years of fenamiphos treatment were applied to an orchard in Crows Landing. No yield benefit and harvests were not collected was attributable to the treatments in 985 in 986. There was no visual benefit from the treatments in 986. n Figure 4 we depict the long term control of root lesion nematode in the surface 24 inches of soil. Tremendous variability occurred among the 5 replicates. The best treatment which reduced root lesion population by 5% was the 5 separate treatments of fenamiphos through the sprinkler system. The dripperapplied treatments had some slight benefit in nematode control. The painting of technical Nemacurwith DMSOonto the trunks four times in the year had no benefit. Ring nematode popuatns were not effectively reduced by any of the fenamiphos treatments. Nemacur is probably worthy of retesting again in orchard with only root lesion nematode as their major problem. CONCLUSON Nine key findings have been made:. The major limitation to walnut growth in replant situations is not the old roots, old leaves or rhizosphere organisms of soil. Each of these components can deter somewhat from plant growth but none are as important a deterrent as root lesion nematode. Damageby root lesion nematode in these tests was 5% (regrowth of Treatment N versus F) in Black walnut. 2. A solid treatment of,3d or MBcan deter root lesion populations in old walnut soil for 2 full years at the 99% control level. The trees also grow uniformly. Unfortunately, walnut trees do notgrow as well as they should in fumigated soil. n situations where we added back a small amount of soil (2 kg/tree) from a recently fumigated orchard the trees did not grow as well as they did when non fumigated soil was added to the tree sites (treatment T versus treatment F). The loss in growth due to fumigation is about 5% in Black Walnut. 3. Root knot nematode was not a deterrent to growth of Black Walnut. To the contrary it was associated with the bestgrowing trees. Since we do not see root knot in established commercial situations there myst be some gradual induction of resistance to root knot in older trees. 4. Some walnut trees can be coming in from nurseries already infested with root lesion. 5. Horticuturaists have indicated there must be some advantage of Paradox over Black or English in the presence of root lesion nematode. n these tests we had an opportunity to compare the three stocks with and without root lesion nematode. Unfortunately, the root lesion contaminated Paradox foiled a good clean look at their differences without root lesion nematode, but in the presence of root lesion nematode only Paradox grew significantly greater than Black which grew significantly better than English. Where root lesion and walnut soil were the inocula Paradox grew significantly better than Black or 88

4 English providing at least 35%more regrowth in 986. The three stocks grew quite similarly if the Paradox was infested with root lesion but Black and English were not. 6. Walnut is an excellent host for root lesion nematode. 7. n the absence of root lesion nematode or in its presence the problem of growing walnuts after peach is greater than growing walnuts after walnuts. 8. For 3% greater tree growth and uniformity in should receive solid preplant treatment and each nonfumigated soil without root lesion nematode. soil in the future. replant situations the soil tree site in9cuated with a We will be working with K43 9. Postplant control of root lesion nematode is possible but may not give yield benefit. 89

5 .~~~~~~~~~~~~~~~~i L ~ Figure. Nematode development and tree resronse following addition of various inocula to Balck Walnut trees planted in fumigated soil. NOCULALTOFUMGATEDSTES TREEGROWTH(Kg) NEMATODEPOPULATONS/25cc \ TMNT. # SOL ROOTS NEMATODESOTHER Regrowth Root lesion Root knot E Walnut Root knot 6. a 2. a 3..' 22.7 K Peach Root knot 5.8 ab. 9 ab T K43 (never fumigated) 5.7 abc.55 abc D Walnut 5.64 abc.72 abc Q Walnut 5.55 abc.76 abc 68.. R Walnut 5.3 abc.5 abc 9..2 (heated at 6 F) M Walnut 5.27 abc.62 abc 59.. leaves Peach 5. abc.5 abc 85.. F 4.95 abc.5 abc L Fumigated 4.77 abc.68 abe 56.. peach A Walnut Root lesion 4.6 be.2 c, S Walnut Root lesion 4.54 be.3 be,569.. N Root lesion 4.5 be.28 be 2,456.. G Peach Root lesion 4.39 e.4 e,896.. Y Walnut trees were removed in spring 983, fumigated with 5 gpa Tene, fallowed soil in 984 and planted to NC Black Walnut seedlings in spring 985.

6 ~,& ~ ~ L & L ' ' L i L i L L. ' ' L ~ i Figure 2. Nematodedevelopment and tree growth following addition of various inocula to Eureka or Paradox walnut seedlings planted in fumigated soi./ t. NOCULATO FUMGATEDSTES TREE GROWTH(kg) OCT., 986 NEMATODEPOPULATON/25cc TMNT SOL ROOTS NEMATODES REGROWTH ROOTLESON Eureka Seedlings (9 reps only) U K43 (never fumigated) H Peach Root lesion o Root lesion B Walnut Root lesion 4.43a 3.57 b 3.52 b 3.4 b NS \D ' Paradox Seedlings C P R (seedlings contaminated with root lesion at Peach Root lesion 5.4 Walnut Root lesion 5.5 Root lesion 4.93 K NS planting) NS " / Twentyyear old walnut tree? were removed in Spring 983, fumigated with 5 gpa Tene, soil fallowed in 984 and planted to Eureka or Paradox seedlings in Spring 985.

7 .a..~ ~ &.& L. & L. L L L. L., L i im.i Figure REGROWTHN KG/TREE (9 reps only) g; NOCULA PARADOX.!.! BLACK EUREKA Walnut soil with root lesion. 89a.5 b.6 b,. Peach soil with root lesion NSroot lesion only. 7la.27 b.98 c K43 soil, no nematodes NS \ N / Paradox seedlings were contaminated at the time of planting with root lesion nematode. f/ Since the th rep of the Eureka seedlings was not available we discarded the th rep from Paradox and Black Walnut also. NOTE: Tree weight~ in separate columns are different at the 5% confidence level if followed by a different letter.

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