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Title: Controlling fusarium wilt of California strawberries by anaerobic soil disinfestation

item MURAMOTO, JOJI - University Of California
item SHENNAN, CAROL - University Of California
item ZAVATTA, MARGHERITA - University Of California
item TOYAMA, LUCINDA - University Of California
item HEWAVITHARANA, SHASHIKA - Washington State University
item Mazzola, Mark

Submitted to: International Conference on Methyl Bromide Alternatives and Emissions Reductions
Publication Type: Proceedings
Publication Acceptance Date: 9/12/2015
Publication Date: 11/8/2015
Citation: Muramoto, J., Shennan, C., Zavatta, M., Toyama, L., Hewavitharana, S.S., Mazzola, M. 2015. Controlling fusarium wilt of California strawberries by anaerobic soil disinfestation. International Conference on Methyl Bromide Alternatives and Emissions Reductions. p. 16.1-4.

Interpretive Summary:

Technical Abstract: In the 2014-15 season, the ASD-treated berry acreage exceeded 1,000 acres in California; more than doubled from the previous season. Fusarium wilt an emerging lethal disease of strawberries in California, can also be controlled by ASD. However, a study has shown that higher soil temperatures are necessary to control this disease by ASD (> 300 cumulative hours above 86 °F at 8” soil depth during the treatment. In the 2013-14 season, we demonstrated that ASD summer flat treatment using 9 t/ac of rice bran and clear TIF can exceed the temperature threshold resulting in reduced F.o.f. soil densities and disease symptoms at Watsonville, CA. However, fruit yield was reduced by the flat ASD treatment, likely resulting from an unexpectedly low-N supply from the added rice bran. Here we report on the 2014-15 trial at the same site that aimed to: 1) demonstrate whether ASD summer flat (ASD-flat) treatment can consistently control Fusarium wilt of strawberries, 2) monitor the effect of ASD-flat on soil N dynamics and 3) examine whether changes in soil microbial community composition are responsible for soilborne disease suppression by ASD in the field trial. Field trial: A replicated trial included ASD-flat with rice bran 9 t/ac (ASD-flat RB9), ASD-flat with molasses 6 t/ac (ASD-flat-ML6), chloropicrin 300 lbs/acre (Pic 300) and untreated check (UTC) as main plots, and with and without pre-plant fertilizer (PPF) as sub plots was established on a sandy-loam Monterey Bay Academy (MBA) site infested with F.o.f. For ASD-flat-RB9 plots, rice bran was broadcasted, rotor-tilled, and TIF clear tarp and 7 lines of drip tapes applied on September 3. A total of 3.3 ac-in of water was drip irrigated from September 3 to 26. For ASD-flat-ML6 plots, molasses was injected via drip tapes with 5.9 acre-inches of water on Sep 3 and 4. On October 23, beds were listed and pre-plant fertilizer (1,000 lbs/ac of 18-8-13, 7-9 months slow release) was shanked into beds of PPF sub plots. Strawberry cv. Albion was planted on November 18. Unlike the 2013-14 season, due to the late start of the treatment, soil temperatures in ASD-flat-RB9 barely reached the cumulative temperature threshold and did not reach the threshold in ASD-flat-ML6 where additional water was used to inject molasses. As a result, ASD treatments did not reduce F.o.f. in the soil compared to UTC regardless of type of C-source whereas Pic 300 reduced poplations significantly (Figure 1 right). Reflecting the soil F.o.f level, wilt score (1: healthy – 5: 76-100% leaves dead) was lowest for Pic 300 and no difference was observed between ASD and UTC though use of PPF slowed disease progression until May. Pic 300 possessed the highest yield, while yields for ASD-flat-RB9 was ~50%, and ASD-ML6 and UTC was ~30% of Pic 300. Soil inorganic N dynamics in 0”-6” soil in ASD-RB9 plots during the growth season showed a similar low level with the previous season. Changes in soil inorganic N distribution across the soil profile (0”-24”) before and after the flat ASD treatment indicated mineralized N accumulation in the subsoil (6”-12” depth) rather than top soil (0”-6” depth) (data not shown). T-RFLP analysis indicated that a distinctive soil bacterial community was formed by each main treatment immediately post-treatment though it did not affect the soil F.o.f. population. In summary, to reduce Fusarium wilt by ASD, summer flat ASD must start by mid-August at latest in the central coast of CA. Another field study found that ASD with a higher rate of C-source (e.g. 15 tons/ac d.w. of grass) can suppress Fusarium oxysporum under soil temperatures similar to those experienced in the central coastal CA (Mazzola,, unpublished). In controlled environment experiments, ASD with grass effectively suppressed populations of an introduced Fof isolate and suppressed wilt. Feasibility and effectiveness of suc