Integrated Phytophthora blight management in vegetable crops with enhanced soil health from cover crops, reduced tillage, and brassica biofumigation

Integrated Phytophthora blight management in vegetable crops with enhanced soil health from cover crops, reduced tillage, and brassica biofumigation

Summary

Healthy butternut squash atop rolled rye mulch in reduced tillage treatment, Hudson Valley, 2016.

The crop disease Phytophthora blight (PB) is a potentially devastating disease and top concern for vegetable growers in the Northeast (including the northeastern Midwest) where susceptible cucurbit and nightshade species of crops contribute to major portions of farm incomes and to the greater vegetable industry. Soil health improvement has been proposed as a fundamental component of an integrated PB and general soil-borne disease management program. Certain brassica cover crops are capable of providing biofumigation services to soils with high soil-borne pathogen loads, and reduced tillage (RT) can allow for soils to regenerate functions that further mitigate soil-borne diseases. This project is aimed at increasing grower awareness and adoption of integrated PB and general soil-borne disease management through demonstration and research trials that combine the novel components 1) of biofumigation with brassica cover crops and 2) reduced tillage (RT) on six NY farms and at Cornell’s Long Island Horticultural Research and Extension Center (LIHREC).

By the end of 2015, seven collaborating growers had completed a total of 13 on-farm trials with brassica cover crops for biofumigation. Throughout winter 2016, biofumigation information and preliminary 2015 trial results were disseminated to a minimum of ~285 growers via educational events. In 2016, four remaining grower collaborators (from trial year 2015) followed their biofumigation trial year with RT treatments; one grower in Long Island opted out of the RT trial year, and two former grower collaborators from western New York failed to successfully implement the RT component at their sites.

All four collaborating growers successfully completed a RT vs. “grower standard” control comparison with a cucurbit response crop across nine total replications. The research team collected data on cover crop biomass, yield, PB incidence, soil infiltration rates, and a soil health assay in 2016. Similar to 2015, weather was not conducive to a proliferation of PB at the trial sites. Phytophthora incidence was therefore low, and, at most sites, non-existent; our ability to collect evidence of treatment effects related to Phytophthora was therefore reduced again in 2016. Results will be analyzed and educational materials developed throughout 2017. In addition to growers that tried brassica cover crops for biofumigation in 2015 (see 2015 report), 2-3 more growers in the Hudson Valley region were noted to have informally tried ‘Caliente’ mustard for biofumigation for the first time in 2016 as a result of this project. 

Objectives/Performance Targets

Accomplishments/Milestones

Impacts and Contributions/Outcomes

Data collected in 2016 will be analyzed throughout 2017. The four remaining on-farm grower collaborators largely did not face difficulty implementing reduced tillage (RT) treatments, even if it was their first time doing so. Typical to the strategy of RT, though, equipment remains a palpable restriction to potential adoption. One collaborating grower needed to borrow equipment from a neighbor, while another borrowed equipment that was available for public demonstration through an unrelated soil health initiative. The latter grower-collaborator plans to purchase RT equipment for the upcoming season; this trial was the first time they used RT strategies. This grower remarked also on how well it worked to suppress weeds compared to their typical approach to weed control. All growers in 2016 were encouraged to, and did, plant rye before their cash crops in 2016, so RT treatments were all mowed into rye stubble or a rolled rye mulch.If applicable, a well-managed rolled cereal cover (especially rye) can be a considerably effective weed suppression component in RT systems (see figure below). Reduced tillage generally suffers from a stigma that it’s risky for weed control because of the loss of cultivation strategies, and sole reliance on herbicides for weed control. One of the original collaborating growers from the Long Island region who opted out of the RT trial portion in 2016 actually did so out of fear of poor weed control in their u-pick pumpkin operation. 

Close-up of a robust reduced tillage rolled-rye mulch (left picture), and trial site illustrating weed suppressive rye mulch (without herbicide) on the left hand side of the picture on the right. The right hand side of the picture on the right is melons growing in standard tillage-based plasticulture beds without a cereal mulch in the inter-rows.

Growers used different types of methods to kill their rye cover crop, though the most common was to combine an herbicide application and a rolling (flattening) with a cultipacker/roller harrow, though one grower used a roller-crimper (specifically designed to eliminate the need for the herbicide component in creating a cover crop mulch). Timing the rye-kill operation is often difficult for growers; it is generally advised to wait until after anthesis/flowering before trying to kill rye. Several growers needed extra unanticipated measures to kill their rye cover. Some had to roll more than once or mow rye that stood back up, or apply herbicide after roller crimping. There were also variations in the density of the stands of rye at various sites. As expected, sites with thicker stands of rye overtly had thicker, more tenacious mulch layers that helped suppress weeds and keep cucurbit fruits from contacting soils. It is also worth noting that although Phytophthora blight (PB) incidence was very low across all sites in 2016- when PB was found on cucurbit fruits, it overwhelmingly seemed to appear where rye mulches were thin or absent and soils had direct contact with the fruit. 

Phytophthora blight incidence in areas where rye mulches were thin and soil contacted the fruit (left and center pictures). The picture on the right illustrates pumpkins lying atop a robust, in-tact rye mulch layer in reduced tillage treatments, protected from contact with soils that may contain Phytophthora spores.

The loss of research sites in western NY was unfortunate and had more to do with communication gaps between multiple managers at each collaborating farm and Extension. The western NY region nonetheless has been the most difficult region to recruit collaborating growers due to 1) fear of disease transfer and crop insurance issues with brassica cash crops and 2) lack of farmers with RT equipment and experience. The research team is attempting to rectify the loss of the research sites and information with a intensified focus on educational events on the project components there throughout 2017. If funding allows, we may also attempt to get an area farm to plant a demonstration plot of a biofumigation cover crop and/or host a RT equipment demonstration for a summer event. 

Trials at the Long Island Horticultural Research and Education Center (LIHREC) were largely successful but they did battle considerable drought again in 2016, similar to the 2015 growing season. Our most novel (i.e. experimental) treatment at the LIHREC, ‘Nemat’ arugula with white clover undersown (with cash crops zone-tilled into the clover living mulch), failed in spring 2015, and was reformulated (to a late summer/fall mustard undersown with white clover) but failed again- both times due to poor clover establishment on the LIHREC’s coarse, droughty soils. It will remain unknown if this treatment would have been viable with good clover establishment, but it highlighted that clover establishment was very sensitive to a lack of soil moisture. Higher seeding rates may also have helped with clover establishment resiliency. This treatment was hence again reformulated in 2016 as a spring sown mustard crop that was rolled after flowering, and then zone tilled into for cucurbit plantings. This treatment was therefore able to combine brassica/biofumigation cover crops and RT in a single season. 

To date, multiple growers outside of the trial research sites have tried brassica/biofumigation cover crops, and the reserch team has so far disseminated project-related information to a minimum of ~525 growers and stakeholders throughout the greater northeast. We anticipate an increases impact towards our performance target in 2017 after disseminating the final results of the project and conducting a formal survey of growers in each region on adoption of integrated Phytophthora blight and general soil-borne disease management, biofumigation with brassica cover crops, and RT. 

Collaborators: