Author: Brian

Exploring Alternative Strategies for Nematode Management in Processing Carrots

By Elisabeth Darling, Sita Thapa and Marisol Quintanilla, Michigan State University

Plant-parasitic nematodes (PPN) alone can cause approximately $80 billion of annual crop loss worldwide. Root lesion nematodes (Pratylenchus spp.) are considered to be the third most economically important PPN in relation to their impact on crops, behind cyst nematodes and root-knot nematodes.

Historically, carrot growers have associated severe PPN damage with the root-knot nematode (Meloidogyne spp.) and, in some cases, the carrot cyst nematode (Heterodera carotae). However, more recently, the root lesion nematode (RLN) has become more prevalent in carrot fields, especially in mineral soils in Michigan.

The economic threshold for RLN is 50-100 nematodes per 100cc of soil. At these levels, RLN can result in the production of unmarketable characteristics such as stubby and forked carrots (Fig. 1).

Currently, the grower standard for PPN control in carrots is Vydate (oxamyl), which has shown reliable suppression of RLN. In 2016, Vydate became unavailable for the growing season, leaving many growers without reliable control for PPN. This incident emphasized the need for a reliable alternative to Vydate for nematode suppression.

In response, a flood of biologically based nematicides have become available to growers. However, the effectiveness of many of these new products has not been sufficiently evaluated. This highlights the necessity of evaluating alternative methods of control, specifically focusing on biological nematicides, incorporating compost and cover cropping using non-host plants.  

Field Trial Results

For the past three years (2017, 2018 and 2019), the applied nematology laboratory at Michigan State University evaluated a list of chemical and biological compounds (Table 1) to manage nematodes in carrot plantings located in Hart, Michigan. In 2017, Vydate increased marketable yield in carrots. In 2018, carrot yields across all treatments (~40 tons/acre) were significantly higher than 2017 (~15 tons/acre). MeloCon was the only treatment that had a lower number of RLN than the control at 21 days post-application. In 2019, nematode pressure was considerably lower than in the past two years (>15 nematodes per 100cc). No trends existed across all three years. However, all treatments reduced nematode counts compared to the untreated control. The Layer Ash Blend (LAB) treatment produced the highest total yield in 2019, followed by a combination treatment of LAB and Vydate.

In addition to nematicide trials, our lab is beginning to evaluate non-host cover crops to reduce RLN. Thus far, we have evaluated multiple cover crops in growth chamber assays. Results indicate that the oilseed radish cultivars “Control,” “Concorde” and “Select,” as well as Dwarf Essex Rape are poor hosts of RLN. All the poor host cover crop cultivars from the growth chamber screening will be evaluated in carrot fields for nematode management in summer 2020.

Chemicals for Nematode Management

Over the past three growing seasons, we aimed to determine the efficacies of popular alternatives to Vydate. In the field trial established throughout the growing seasons of 2017, 2018 and 2019 in Hart, Michigan, plots were arranged in a complete randomized block pattern, and each treatment was replicated five times. Chemical or biological treatments (Table 1) were applied in the following ways: pre-plant (compost), in-furrow (Velum Prime, MeloCon, Majestene) and hand-held sprayer prior to plant (Nimitz). Soil samples were collected four times throughout the season: initial, 21-day post-application, mid-season and harvest. Soil samples were processed to identify nematode populations and diversity. A 1-meter row of carrots was selected within each plot to harvest and evaluate. Carrots harvested went through grading based on USDA standards, and each carrot was evaluated for nematode damage. 

Despite seeing some trends between years, no treatment showed to have a significant reduction of unmarketable characteristics or yield comparable to Vydate. The turbulent 2019 field season proved to show considerable challenges for farmers and researchers. Although it is notable to mention that while not significantly, all treatments did outperform the untreated control plots in nematode reduction. For this reason, we are evaluating a new selection of biological nematicides, as well as performing preliminary evaluations on potential cover crops.

Cover Crops as Sustainable Strategy

As a non-chemical alternative, cover crops including oilseed radish (OSR) have been shown to reduce plant-parasitic nematode populations. Several studies have shown that OSR cover crops not only reduce nematode populations but also suppress weeds, recycle nitrogen and significantly improve carrot yields. Carrot growers feel OSR is an ideal cover crop because it winter kills, leaves behind less residue than other cover crops and provides a nice, “mellow” seedbed for the small-seeded carrots.

To qualify as a good cover crop for the management of plant-parasitic nematodes, the crop should be a poor host for the nematodes, thereby lowering the population after incorporation of the crop into the soil. Our main objective with this project is to identify excellent cover crop cultivars for the management of nematodes.

In growth chamber trials, we evaluated the host status of 10 OSR cultivars, tillage radish and Dwarf Essex Rape for the RLN. We found that OSR cultivars “Control,” “Concorde” and “Select” and Dwarf Essex Rape (Fig. 2) are poor hosts of RLN.

Currently, another trial for root-knot nematode is ongoing. This project is in the starting phase; however, results indicating poor hosts of both lesion nematode and root-knot nematode will be evaluated in carrot fields in summer 2020.

The U.S. Department of Agriculture’s National Institute of Food and Agriculture (NIFA) announced that it is investing in research on the impact of COVID-19 on American agriculture. Last week, NIFA opened its request for applications on research or extension activities that focus on developing and deploying rapid, reliable, and readily adoptable COVID-19 agricultural strategies across the food and agriculture enterprise. Through the Agriculture and Food Research Initiative (AFRI) program, NIFA will invest up to $9 million for research in the following areas: : health and security of livestock; food and food processing; well-being of farm workforce, food service providers, and rural Americans; and economic security. Applications are due June 4, 2020. “Keeping the agricultural workforce healthy and our nation’s food supply safe is a top priority for USDA,” said Scott Angle, NIFA Director. “The entire country depends on the jobs that these agricultural workers do, from farm to fork, to ensure a robust agricultural food supply. The systems that our agricultural workforce manages and the products they produce literally sustain both our bodies and our nation’s economy.” NIFA is using an expedited solicitation, evaluation, and grant-making process to quickly deploy funding on COVID-19 agricultural research. In turn, the agency will only fund projects designed to swiftly fill knowledge and information gaps; strengthen and support critical cross-cutting issues to protect the food and agriculture supply chain, livestock health and security, the safety of our foods; as well as research projects that focus on the well-being of farm, food service providers, and rural Americans. “Every step must be rapid,” said Angle, “so we can use agricultural sciences to mitigate this crisis.” In response to the current Pandemic, NIFA also set a deadline of May 21, 2020, for COVID-19 research proposals from all other areas in the wide-ranging AFRI request for applications (RFA). NIFA also re-opened its Small Business Innovation Research RFA to search for COVID-19 solutions from small businesses. NIFA invests in and advances agricultural research, education, and extension, and promotes transformative discoveries that solve societal challenges. NIFA’s integrated research, education, and extension programs support scientists and extension personnel whose work results in user-inspired, groundbreaking discoveries. These discoveries combat childhood obesity, improve and sustain rural economic growth, address water availability issues, increase food production, find new sources of energy, mitigate climate variability, and ensure food safety. To learn more about NIFA’s impact on agricultural science, visit https://nifa.usda.gov/impacts, sign up for email updates or follow us on Twitter @USDA_NIFA, #NIFAimpacts.

Cal-Organic Farms is now shipping organic red bunch carrots from Coachella, California. A division of Grimmway Farms, Cal-Organic is offering the carrots for a limited time. The California-grown carrots are available in 12- and 24-count cases with green tops intact.

The company bills the carrots as an excellent source of vitamin A with sweet flavor. With solid red color through the root, the carrots are favored by shoppers for their colorful appearance and their vibrant presentation on the plate, the company says.

Supplies are expected to last until the end of March.

Establishing a Carrot Cavity Spot Nursery at Washington State University

By Lindsey du Toit and Michael Derie, Washington State University

 

Why Set up a Cavity Spot Nursery?

Cavity spot occurs in almost all regions of carrot production. This disease is listed by the California Fresh Carrot Advisory Board (CFCAB) as one of the primary concerns for carrot growers in California, who produce 70 percent of the fresh market carrots in the U.S. The pathogens associated most commonly with cavity spot are Pythium violae and P. sulcatum, but other species of Pythium can cause this disease.

These are not true fungi, but water molds (oomycetes). These pathogens survive in soils where they produce two kinds of spores: long-lived, sexual spores called oospores, and short-lived, swimming spores called zoospores. The oospores are triggered to germinate by chemicals that roots of plants exude into the soil. The pathogens are most active and usually cause the most damage in cool, moist soil conditions.

Cavity spot seldom causes a reduction in overall carrot root yield (weight or size of roots). However, the disease can have a very significant economic impact for growers because the shallow, sunken lesions caused by the pathogens on the surface of roots make the roots unmarketable for fresh or processing markets (Fig. 1). The lesions on roots start as very small (a few millimeters in diameter), sunken areas that can increase to more than 1 inch in length.

 

 

Pythium species usually infect carrot roots within four to six weeks after planting, but infection can continue as long as roots remain in the soil. Cavity spot usually increases the longer carrot roots are left in the soil. The disease will even continue to develop on roots that have been harvested and placed in storage. The lesions or cavities on the roots can be invaded by secondary microorganisms, including bacteria. This can cause the cavities to become discolored, particularly during heating/blanching of carrots being processed (Fig. 2).

 

 

Growers often struggle to manage cavity spot using cultural practices and fungicides. Recommendations to control cavity spot include avoiding fields with a history of the disease, using a crop rotation of at least three to four years between carrot crops, not using high rates of nitrogen fertilization, planting in fields with good drainage that is less favorable for the swimming spore stage, not planting in cold soils and harvesting roots in a timely manner to limit development of cavity spot. Some fungicides can be highly effective against cavity spot, such as metalaxyl or mefenoxam (e.g. Ridomil). Unfortunately, the pathogens that cause cavity spot are notorious for developing resistance to fungicides like mefenoxam, which severely limits the ability for growers to control cavity spot using fungicides.

Given the difficulty of managing cavity spot, many seed companies are trying to breed for resistance to the disease, but the process is not easy and progress has been slow. There are differences in susceptibility to cavity spot among commercial cultivars, but there are no cultivars that are completely resistant to the disease. Carrot growers in some states continue to fund Phil Simon, USDA-ARS carrot breeder based in Madison, Wisconsin, to develop cultivars with better resistance to cavity spot. Simon has been collaborating with Mary Ruth McDonald, plant pathologist at the University of Guelph in Ontario, Canada, in efforts to breed for resistance to cavity spot. McDonald has established a cavity spot nursery in a muck soil in Ontario that is naturally infected with cavity spot pathogens.

In most regions of carrot production in the U.S., the soils are sandy/mineral, so growers in California have been wanting to create a cavity spot nursery in a field with mineral soil. In 2019, the CFCAB provided funding to Lindsey du Toit’s program at Washington State University (WSU) to establish a cavity spot nursery at the WSU Mount Vernon Northwestern Washington Research & Extension Center (NWREC) in Mount Vernon, Washington, to complement the muck cavity spot nursery in Ontario and provide further support for Simon’s efforts at breeding for resistance to this disease.

 

How to Establish a Cavity Spot Nursery

To establish the cavity spot pathogens in the field site in Mount Vernon, a 1-acre field was fumigated with metam sodium in fall 2018 to kill microorganisms in the soil that might compete with cavity spot pathogens. The field was then inoculated with P. violae and P. sulcatum three weeks later. The inoculum was produced by growing the pathogens on vermiculite moistened with V8 juice (Yes, Pythium species like V8 juice as much as some people like Bloody Marys!) in mushroom bags. About 250 gallons of inoculum were spread over the field using a tractor mounted, PTO-driven, Viton sling spreader (Fig. 3). The inoculum was incorporated into the soil by rototilling. The field was inoculated again with 266 gallons of inoculum of P. violae and P. sulcatum in April 2019.

 

 

On May 3, 2019, 219 carrot breeding lines and 12 commercial carrot cultivars were planted in replicate blocks in the field. The cultivar Atomic Red, which is highly susceptible to cavity spot, was planted throughout the trial as a susceptible check to assess the uniformity in cavity spot pressure across the field. Each plot was a single row, 10 feet long. Rows were spaced 20 inches. The seed for each plot was planted using a Wintersteiger cone push planter set to distribute 100 seeds in each plot. The trial was irrigated 19 times between May and early September to promote carrot root growth and development of cavity spot.

In September 2019, each plot was rated for the percentage of plants that had bolted (started flowering) and for average height of the plants. In October 2019, the roots in each plot were undercut, dug manually, washed and rated for the percentage of roots in each plot with symptoms of cavity spot and the severity of symptoms on each root based on the size of the largest lesion on each root (Fig. 4, Fig. 5).

 

 

 

Success at Establishing the WSU Carrot Cavity Spot Nursery

Cavity spot symptoms were observed on all but eight of the 231 carrot lines evaluated, including all 12 named cultivars. Isolations from root lesions confirmed the symptoms were cavity spot, as Pythium was isolated from all of the lesions tested. There was a wide range in incidence and severity of cavity spot among the 231 lines, which demonstrated success at establishing the WSU Carrot Cavity Spot Nursery. For the 231 carrot entries evaluated, the percentage of roots with cavity spot ranged from 0 to 100 (average of 33.6 percent), and the severity ranged from 0 to 79 (average of 19.8) (Table 1).

Although cavity spot symptoms were observed on the vast majority of the carrot lines evaluated, for the eight entries with no cavity spot, 50 to 100 percent of the plants had bolted. When plants bolt, the roots turn “woody” and do not show symptoms of cavity spot, as demonstrated by the negative correlation between the percentage of plants bolted and both the incidence and severity of cavity spot. Therefore, the eight lines with a high percentage of bolting and no cavity spot were not included in the data analysis for cavity spot.

Of the 12 carrot cultivars evaluated, the incidence and severity of cavity spot was least on Purple Haze. Based on trials in Ontario and other sites, Purple Haze is partially resistant to cavity spot. In the WSU Cavity Spot Nursery, 11.1 percent of Purple Haze roots had cavity spot lesions, with a mean severity of 3.2 (Table 1). In contrast, the percentage of roots with cavity spot was greatest on Atomic Red, the susceptible control cultivar (42.4 percent of roots had cavity spot, with an average severity of 28.5). Of the other breeding lines and plant introductions (PIs), 26 had fewer roots with cavity spot than Purple Haze, and 13 had less severe cavity spot symptoms than Purple Haze, the partially resistant cultivar. Some of these 13 lines had a lot of bolted plants, which confounded cavity spot ratings, but five of the 13 had no bolted plants. This included PI 225869 (0.3 severity of cavity spot), PI 225870 (1), PI 652188 (2), PI 451761 (2) and 725-1 (2.5). These lines might be valuable sources of resistance to cavity spot. The entries will be evaluated again in 2020 in the WSU Carrot Cavity Spot Nursery to determine the consistency in response of the cultivars. The percentage of roots with cavity spot was significantly correlated with the severity of cavity spot across all the lines tested (r = 0.9154 at P< 0.0001).

 

 

The percentage of plants that bolted ranged from 0 to 100 (average of 15.9 percent) and was particularly severe for some PIs. None of the named cultivars had bolted plants, except for Purple Haze, which only had 2.5 percent bolted plants. Carrot rust fly pressure was also quite severe in the trial.

 

What’s Next?

After rating the carrot roots in October, the roots were spread out on the field and disked into the soil to increase cavity spot pressure for planting another trial in 2020. In addition, a third batch of inoculum of P. sulcatum and P. violae was produced on vermiculite with V8 juice, applied to the field in October 2019 and incorporated into the soil. The field will be inoculated again in spring 2020 to continue building cavity spot disease pressure for this nursery. This nursery will support the development of carrot cultivars with improved resistance to cavity spot.

The 2020 WSU Carrot Cavity Spot Nursery trial will be included in the field tour as part of the 40^th International Carrot Conference on Oct. 5-6, 2020, at the WSU Mount Vernon NWREC. For more details on that conference, visit www.internationalcarrots.org.

 

Cal-Organic Farms is now shipping organic red bunch carrots from Coachella, California. A division of Grimmway Farms, Cal-Organic is offering the carrots for a limited time. The California-grown carrots are available in 12- and 24-count cases with green tops intact.

The company bills the carrots as an excellent source of vitamin A with sweet flavor. With solid red color through the root, the carrots are favored by shoppers for their colorful appearance and their vibrant presentation on the plate, the company says.

Supplies are expected to last until the end of March.

 

Automated Produce Equipment (APE) based in Atlanta, Georgia will be exhibiting at the Potato Expo in Las Vegas, Nevada at the Mirage Convention Center, January 14-15, 2020. APE provides engineered solutions from bin tipping to packaging and robotic palletizing at the end of the packing line.  APE offers quality machinery designed to reduce labor, increase efficiency, and keep customers competitive. Although APE’s focus is primarily on potatoes, onions and carrots they also provide equipment packaging, and solutions for all other crops. Mike McKnight, APE’s owner and president has been a provider of produce packaging equipment for nine years. Mike is well-acquainted with the industry and can address each individual company’s needs. Customers looking for one machine, or a complete line can find everything they need at Automated Produce Equipment by stopping by  Booth #421 or visit APE’s website  www.automatedproduceequip.com or, email Mike McKnight  at mike@automatedproduceequip.com or, call  678 383-4566.

The U.S. Department of Agriculture (USDA) and the Office of the United States Trade Representative (USTR) are accepting applications for new members to serve on seven agricultural trade advisory committees.

Members of the Agricultural Policy Advisory Committee (APAC) advise USDA and USTR on operating existing U.S. trade agreements, on negotiating new agreements, and on other trade policy matters. Members of six Agricultural Technical Advisory Committees (ATACs) provide technical advice and guidance on international trade issues that affect both domestic and foreign production in specific commodity sectors. The ATACs focus on trade in:

• Animals and animal products;
• Fruits and vegetables;
• Grains, feed, oilseeds and planting seeds;
• Processed foods;
• Sweeteners and sweetener products; and
• Tobacco, cotton and peanuts.

To be considered for candidacy, applicants must have significant expertise in both agriculture and international trade matters. Committee members, who serve four-year terms, represent a cross-section of U.S. food and agricultural stakeholders. They must be U.S. citizens, qualify for a security clearance, and be willing to serve without compensation for time, travel or expenses. The committees hold frequent conference calls and generally meet in Washington, D.C., twice a year.

Application instructions are available at https://www.fas.usda.gov/trade-advisory-committees-applying-membership. Applications must be received by 5 p.m. ET on January 31, 2020. Any applications received after the deadline will be considered for future appointments as appropriate.

For more information, visit www.fas.usda.gov/ATACs or e-mail ATACs@fas.usda.gov.

The Idaho Association of Plant Protection (IAPP) has a meeting scheduled for Wednesday, November 6, at Canyon Crest in Twin Falls starting at 1 PM going through 5 PM.

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