Posts Tagged: soilborne
Impact of drip application of fungicides on strawberry health and yields
Strawberry, a high-value specialty crop in California, suffers from several soilborne, fruit, and foliar diseases. Verticillium wilt caused by Verticillium dahliae, Fusarium wilt caused by Fusarium oxysporum f. sp. fragariae, and Macrophomina crown rot or charcoal rot caused by Macrophomina phaseolina are major soilborne diseases that cause significant losses without proper control. Chemical fumigation, crop rotation with broccoli, nutrient and irrigation management to minimize plant stress, and non-chemical soil disinfestation are usual control strategies for these diseases. Botrytis fruit rot or gray mold caused by Botrytis cineaea is a common fruit disease requiring frequent fungicidal applications. Propagules of gray mold fungus survive in the soil and infect flowers and fruits. A study was conducted to evaluate the impact of drip application of various fungicides on improving strawberry health and enhancing fruit yields.
Methodology
This study was conducted in an experimental strawberry field at the Shafter Research Station during 2019-2020. Cultivar San Andreas was planted on 28 October 2019. No pre-plant fertilizer application was made in this non-fumigated field which had Fusarium wilt, Macrophomina crown rot, and Botrytis fruit rot in previous year's strawberry planting. Each treatment was applied to a 300' long bed with single drip tape in the center and two rows of strawberry plants. Sprinkler irrigation was provided immediately after planting along with drip irrigation, which was provided one or more times weekly as needed for the rest of the experimental period. Each bed was divided into six 30' long plots, representing replications, with an 18' buffer in between. Between 6 November 2019 and 9 May 2020, 1.88 qt of 20-10-0 (a combination of 32-0-0 urea ammonium nitrate and 10-34-0 ammonium phosphate) and 1.32 qt of potassium thiosulfate was applied 20 times at weekly intervals through fertigation. Treatments were applied either as a transplant dip or through the drip system using a Dosatron. The following treatments were evaluated in this study:
i) Untreated control: Neither transplants nor the planted crop was treated with any fungicides.
ii) Abound transplant dip: Transplants were dipped in 7 fl oz of Abound (azoxystrobin) fungicide in 100 gal of water for 4 min immediately prior to planting. Transplant dip in a fungicide is practiced by several growers to protect the crop from fungal diseases.
iii) Rhyme: Applied Rhyme (flutriafol) at 7 fl oz/ac immediately after and 30, 60, and 90 days after planting through the drip system.
iv) Velum Prime with Switch: Applied Velum Prime (fluopyram) at 6.5 fl oz/ac 14 and 28 days after planting followed by Switch 62.5 WG (cyprodinil + fludioxinil) at 14 oz/ac 42 days after planting through the drip system.
v) Rhyme with Switch: Four applications of Rhyme at 7 fl oz/ac were made 14, 28, 56, and 70 days after planting with a single application of Switch 62.5 WG 42 days after planting through the drip system.
Parameters observed during the study included leaf chlorophyll and leaf nitrogen (with chlorophyll meter) in February and May; fruit sugar (with refractometer) in May; fruit firmness (with penetrometer) in April and May; severity of gray mold (caused by Botrytis cinereae) twice in March and once in May, and other fruit diseases (mucor fruit rot caused by Mucor spp. and Rhizopus fruit rot caused by Rhizopus spp.) once in May 3 and 5 days after harvest (on a scale of 0 to 4 where 0=no infection; 1=1-25%, 2=26-50%, 3=51-75% and 4=76-100% fungal growth); and fruit yield per plant from 11 weekly harvests between 11 March and 14 May 2020. Leaf chlorophyll and nitrogen data for the Abound dip treatment were not collected in February. Data were analyzed using analysis of variance in Statistix software and significant means were separated using the Least Significant Difference test.
Results and Discussion
Leaf chlorophyll content was significantly higher in plants that received drip application of fungicides compared to untreated plants in February while leaf nitrogen content was significantly higher in the same treatments during the May observation. There were no differences in fruit sugar or average fruit firmness among the treatments.
Average gray mold severity from three harvest dates was low and did not statistically differ among the treatments. However, the severity of other diseases was significantly different among various treatments with the lowest rating in Abound transplant dip on both 3 and 5 days after harvest and only 3 days after harvest in plants that received four applications of Rhyme. Unlike the previous year, visible symptoms of the soilborne diseases were not seen during the study period to evaluate the impact of the treatments. However, there were significant differences among treatments for the marketable fruit yield. Highest marketable yield was observed in the treatment that received Rhyme and Switch followed by Velum Prime and Switch and Rhyme alone. The lowest fruit yield was observed in Abound dip treatment. Unmarketable fruit (deformed or diseased) yield was similar among the treatments. Compared to the untreated control, Abound dip resulted in 16% less marketable yield and such a negative impact from transplant dip in fungicides has been seen in other studies (Dara and Peck, 2017 and 2018; Dara, 2020). Marketable fruit yield was 4-28% higher where fungicides were applied to the soil.
Although visible symptoms of soilborne diseases were absent during the study, periodic drip application of the fungicides probably suppressed the fungal inocula and associated stress and might have contributed to increased yields. The direct impact of fungicide treatments on soilborne pathogens was, however, not clear in this study. Considering cost of chemical fumigation or soil disinfestation and the environmental impact of chemical fumigation, treating the soil with fungicides can be an economical option if they are effective. While this study presents some preliminary data, additional studies in non-fumigated fields in the presence of pathogens are necessary to consider soil fungicide treatment as a control option.
Acknowledgments: Thanks to FMC for funding this study and Marjan Heidarian Dehkordi and Tamas Zold for their technical assistance.
References
Dara, S. K. 2020. Improving strawberry yields with biostimulants and nutrient supplements: a 2019-2020 study. UCANR eJournal of Entomology and Biologicals. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=43631
Dara, S. K. and D. Peck. 2017. Evaluating beneficial microbe-based products for their impact on strawberry plant growth, health, and fruit yield. UCANR eJournal of Entomology and Biologicals. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=25122
Dara, S. K. and D. Peck. 2018. Evaluation of additive, soil amendment, and biostimulant products in Santa Maria strawberry. CAPCA Adviser, 21 (5): 44-50.
How cultural practices can influence productivity and plant health in strawberry production
This is a presentation I gave at farm advisor Steve Koike's plant disease seminar in Salinas,...
Koik Plant Disease Meeting 11-4-2015
Fusarium Crown and Foot Rot of Squash and Pumpkin Fusarium solani f. sp. cucurbitae Race 1
This post was generated in response to a case of Fusarium crown and foot rot in Sacramento County...
I Have a Diagnosis of Macrophomina or Fusarium in My Strawberry Field – Now What Do I Do?
Accompanying the current spate of Macrophomina and Fusarium discoveries by the UCCE Diagnostic Laboratory in Salinas and by other pathologists, growers, farm managers, and PCAs are now faced with the question of what the next step should be.
Fumigation: The advice for growers and farm managers is to avoid bed fumigation at this juncture. Even beds fumigated by professional operators will have little reservoirs of surviving pathogens on the shoulders where the fumigant did not travel. Of great concern are pathogen populations surviving in the soil making up the untreated furrows. Growers who are not flat fumigating with methyl bromide + chloropicrin should consider using a high rate of chloropicrin under impermeable film. This likely will not be as good a treatment as the mix of methyl bromide + chloropicrin used in the past, but it is the next best soil treatment solution.
Reducing stress to the plants: The diseases caused by both Macrophomina and Fusarium develop earlier, more rapidly, and more severely if plants are stressed. Strawberries that are under-chilled or subject to irrigation deficits, fertility shortfalls, and/or pest issues (such as mites) can succumb fairly rapidly, while those perfectly managed can withstand disease for a longer time. Growers wanting to reduce their diseases losses from here on out will need to play a tight defensive game and address plant stress factors in a timely manner.
Not disturbing the existing bed: The in-field spread of both Macrophomina and Fusarium is mainly accomplished by tillage and other procedures that move soil around. Because neither pathogen makes airborne spores (such as those made by powdery mildew and gray mold pathogens) or swimming zoospores found in soil water (produced by Phytophthora), the spread of inoculum is only by physical movement of the soil. Presumably, beds remaining intact and in place, as they would be for second year strawberries or other system of minimal tillage, will keep the pathogen from being spread to non-infested parts of the field.
This situation has been observed locally. In 2013, a strawberry field had significant Macrophomina outbreaks in certain parts of the field. Held over for a second year, the dead areas were replanted and again developed disease in those sections; however, second year plants that were healthy in 2013 were mostly healthy in 2014. While growing second year strawberries is not being recommended, this type of situation demonstrates the key role of soil movement in disease epidemiology.
Sanitation: Sanitation is critical for limiting the spread of Macrophomina and Fusarium. Tractors, tillage equipment, and irrigation pipes moving from infested fields should be cleaned. Remember too that a strawberry field that had significant dieback two years ago and is now planted to lettuce or another crop, likely still has plenty of Fusarium or Macrophomina around. It is a good practice for all of us to pay attention to where we have been and clean up if you are coming out of an infested field.
Having the Right Attitude and Accept the Changing Reality: In this environment of new diseases and reduced to no availability of good fumigants, those able to keep open minds and adopt new practices stand the best chance to weather the storm from these new pathogens. Growers and agricultural professionals of all stripes MUST adapt to this new era. Go to meetings, keep up to date on the latest research, talk with reputable professionals and be ready to make the changes necessary to keep your crop the most productive it can possibly be.
Photo progression- Field with Macrophomina June 21. Photo by Steven Koike, UCCE.
Photo progression - same field as above with Macrophomina- July 5. Photo by Steven Koike, UCCE.
Photo progression - Same field as above with Macrophomina July 26. Photo by Steven Koike, UCCE.
Survey of Research and Extension in Strawberry Soilborne Diseases
I'm asking you as my readers to participate in a survey concerning soilborne pathogens in strawberries and caneberries. There's a few questions about what your expectations are in managing these, as well as a number of questions concerning how and where you normally obtain information on these matters.
I've taken it already, and find it to be a well thought out survey which takes about 5 minutes to do. I'd really appreciate your participation if not only for the two reasons given below.
A few years someone was trumpeting a survey he was party to that determined that UC Cooperative Extension wasn't even in the top five sources of information for growers. That always struck me as pretty strange, because my colleagues and I spend a good part of every day answering agriculture questions, and our meetings usually have a lot of people attend. Our websites don't lack for traffic (I think the UC IPM website alone gets like one million views a month) and we do a brisk business out of our offices distributing pamphlets and selling publications. Something doesn't match up with what that survey from a few years ago said, and so hopefully the survey here will help clarify what is going on and give us an idea of where we can improve our services.
Second, because I'm welcomed on to most ranches (not all though), I think I have a pretty good feel for what is going on with berries on the Central Coast. Quite frankly from what I have seen with my colleagues (especially Steven Koike from the Monterey CE office) over the past two years on the advance of soil pathogens is concerning, and we aren't even completely post methyl bromide yet. And that's the other big part of the survey which explores what you think matters most in soilborne pest management and what you think the scientific community should be doing about it.
But if you don't do the survey, we aren't going to know very much more about either of these.
Here's the link:
http://ucanr.edu/sites/Strawberry_soil-borne_diseases/
Strawberries zapped by Fusarium in May, 2014. Photo courtesy Steven Koike, UCCE.