New Ways To Protect Produce Crops Grown on Plastic Mulch Beds

Plastic mulch beds in Florida

Here is a side-by-side comparison of traditional plastic mulch beds compared to compact bed design. The absence of methyl bromide has spurred growers to get more creative in protecting their crops grown on plastic mulch.
Photo courtesy of UF/IFAS

Methyl bromide is becoming a more distant memory with every passing year. The proverbial silver bullet that took care of many early-season pest problems was phased out in the mid-2000s. Since that time growers have developed strategies to replace the fumigant that took out nematodes, weeds, and soil-borne pathogens.

In 2015, Florida Grower® magazine featured a three-part cover story series looking at various approaches of pest management in plastic mulch crop. Growers and scientists have continued working to find effective replacements to methyl bromide since that time.

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What Took One, Now Takes More

After methyl bromide went away, it quickly became clear that growers’ pest control toolbox was going to get a whole lot bigger. And it would require chemical and cultural approaches. That process is still underway, but much progress has been made.

Johan Desaeger, Assistant Professor of Entomology and Nematology with UF/IFAS, says most growers are now utilizing a combination of fumigants.

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“Many growers are using 1,3-Dichlo-ropropene (Telone) usually mixed with chloropicrin and metam,” Desaeger says. “More growers are starting to use non-fumigant nematicides like Nimitz (fluensulfone, ADAMA) and Velum (fluopyram, Bayer).”

The non-fumigant products have gained in popularity as part of an overall nematode management program for the ease of handling and safety profile. They also do not fall under the regulations requiring a fumigant management plan.

When it comes to nematodes, research has uncovered that the pests can move a lot in the soil, despite their tiny size. Root-knot and sting nematodes can occur at soil depths of 3 to 4 feet. That is well below standard soil sampling depths for nematodes. Those deep nematodes can migrate up toward the root zone (usually in 30 to 45 days) to do damage to the crop. It is important to sample shallow and deep for nematodes and always look for symptoms like root galling.

Deep shank application of Telone for nematodes

Fields with high infestations of nematodes benefit from deep-shank application of Telone.

“For high infestations, broadcast deep-shank applications of Telone are being applied, along with standard bed fumigation,” Desaeger says. “In addition, more nematicides are being developed that should give growers more flexibility with their management programs.”

Mechanical and Cultural Approaches

Getting fumigant products to move through the bed also has been the focus of research. New application tools have been developed that deliver fumigant to the side of the beds. Newer products like Nimitz and Velum can be applied through drip irrigation to target the root zone.

Applying fumigant in good soil conditions (moist, but not too wet) and in timely and properly pressed beds also is important.

Natalia Peres, Professor of Strawberry Pathology with UF/IFAS, has been studying Macrophomina causing crown rots in strawberries. In fields where Macrophomina is a problem, she recommends an integrated management approach with crop termination and fumigation prior to planting. In addition, she recommends not to double-crop on the same plastic to help remove inoculum in the fields. If double-crop is used, she recommends that all crop debris is removed from the field after termination because the plants carry high levels of Macrophomina into the next season.

Some growers with high levels of Macrophomina infestation have begun to remove strawberry crop debris by hand and haul it out of fields in trash bags. That’s an expensive endeavor, but losing more than half of a strawberry crop’s stand is more expensive. The plant removal, along with more tolerant varieties like ‘Sensation’ and good fumigation, has greatly improved crop stands.

Fumigation rig in the field

Researchers have experimented with a number of different rigs and set ups to better apply fumigant to the sides of the bed.
Photo courtesy of UF/IFAS

Peres notes one grower’s experience that was losing 65% of his crop in one highly infested field due to lack of emergence caused by the disease. After taking these steps in combination, the grower’s total mortality rate fell to 2.5% in that field. He believes the plant removal played a significant role in the vastly improved stand.

Dr. Sanjay Shukla, Professor of Agricultural and Biological Engineering with UF/IFAS, has been working with growers on a concept he developed cal-led compact bed geometry (CBG). The research showed improved irrigation efficiency from taking the standard bed height of 6 to 8 inches, and width of 30 to 36 inches, to a taller, narrower configuration. The CBG design takes beds to 10 to 12 inches tall and 16 to 24 inches wide.

Using this design, some growers have been able to cut water usage in half and have been able to use one strip of drip tape for irrigation, rather than two, with no loss in yield or quality. The design also has improved fumigation performance. Other benefits include reduced fertilizer inputs, less plastic mulch required (up to $500 per acre savings in some cases), and better protection from flooding. Two of Florida’s largest tomato growers have gone to CBG design.

Weed Control Tactics

Growers have widened their arsenal when it comes to weed control, as well. Dr. Nathan Boyd, Weed Scientist with UF/IFAS, has worked with growers to develop effective weed management programs.

“One of the biggest shifts since methyl bromide has gone away is that the use of pre-emergent herbicide has now become routine,” Boyd says. “There also has been a transition to totally impermeable film (TIF) mulch in some crops, which enhances fumigant efficacy and also impedes nutsedge emergence.”

While it varies by crop, the most common pre-emergent combination under the plastic is Dual (metolachlor, Syngenta) and Devrinol (napropamide). In strawberries, it is commonly Goal, (oxyflurofen, Dow AgroSciences) and Devrinol or Chateau (flumioxazin, Valent).

“The most common application method is fumigating your beds, then as you press your beds a second time, you have nozzles on the rig applying the herbicide,” Boyd says. “That way you are running pieces already in use in the field — not adding additional equipment. While there are some growers who run a separate herbicide rig or other set-ups, it all depends on if they run the press a second time.”

Purple nutsedge on tomato plants

Nutsedge is the among the most problematic weeds in plastic mulch crops.
Photo by Frank Giles

FMC has a label for Spartan FL 4F (sulfentrazone) for several Florida specialty crops. “It controls a range of broadleaf weeds, but it also is effective on yellow nutsedge,” Boyd adds. “This is a huge advantage for us because we don’t have many herbicides that can control nutsedge in vegetable crops.”

Boyd says Syngenta is developing a new herbicide active ingredient, bicyclopyrone, that looks promising.

“We also are working on getting a few row-middle herbicides registered for use in specialty crops,” he says.

An important weed control tactic is keeping crops healthy. That means starting with healthy transplants or seed with excellent germination. It also means keeping plants properly irrigated along with a good fertility program to help crops compete with weeds.

Cover crops have also become more popular in recent years for a number of benefits. One of those benefits is the prevention of weed germination between crops.

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