Horticultural Crops: The Farmers

Confidence in Postemergence Flaming Comes with Experience, Innovation

Phil Foster
Hollister, California

  • 200 acres (buried drip, sprinkle irrigation)
  • fresh vegetables
  • clay soils and sandy loam soils
  • certified organic
  • cabbage, peppers, fennel, celery, sweet corn, melons, hard squash, garlic, onions

Weed management highlights

Strategies: cultivation... flaming... pre-irrigation... transplanting... cover crops... hand weeding... crop rotation

Tools: low-residue cultivators... precision bed tooling... homemade guidance sled... toolbar flamer... torsion rod in-row weeders... rolling cultivator... disk hillers

Experience is a great confidence builder, and it takes lots of confidence to subject a field of high-value garlic to the cell-bursting heat of a flame weeder. Phil Foster has done it often enough that he feels comfortable seeing blackened greens as he pulls from the field. He knows that the garlic will come back but that the current crop of weeds is history.

His farms include clay (3 to 4 percent organic matter) and sandy loam soils (1.5 percent organic matter) and receive 12 to 13 inches of precipitation annually, mostly from December to March. Careful use of furrow, drip and sprinkle irrigation systems keeps crops green. He uses pre-irrigation to encourage a flush of weeds that he lightly tills out prior to planting - a traditional dryland practice widely used by many farmers, conventional and organic. Running a single, permanent drip line deep below crop rows lets him limit weed growth by concentrating water close to the crop roots. Through careful use of a mechanical spader, he can even till in a cover crop with the drip lines in place.

Foster builds beds that are 40 inches wide and about 5 inches tall to plant a broad mix of vegetable crops in a year-round growing season.

Cover crops improve and protect his soils. Covers include a cereal grain (rye, wheat or barley), Magnus field peas or a mixture of vetch (purple or lana woolypod), peas, bellbeans and oats. Ahead of planting, he flail mows the cover crops then incorporates them with a spading machine or offset disk with 24-inch blades.

He applies carefully managed, often-turned compost produced on his farm to increase fertility and biological activity in soil. The major application - about half a field's yearly total - goes on in the fall to prepare for fall and winter planting. He applies from 9 to 12 tons of compost per acre per year. Even after a cover crop, he applies 5 tons per acre to continue building soil quality.

Preemergence flaming is Foster's most efficient early season weed control. He uses a two-bed toolbar mounted flamer, which has four burners per bed. He orients burners pointing backward, parallel to the direction of the rows. This prevents small weeds from being protected from the flame by the indentation left by packer wheels. Weed escapes in this groove are more likely when flames shoot across from the side.

He concentrates on flaming before crops emerge to purge the seedbed of living weeds, but he uses postemergent heat treatments as he gains experience with timing. Field patches with heavy weed pressure, or fields that didn't receive proper early season control, are postemergent candidates. He estimates he's flamed about 10 per cent of his acres per year post-emerge over the last decade.

Foster considers postemergent flaming as a rescue strategy. In onions, he calculates a 10 to 15 percent production loss from the treatment, which sets the crop back about 7 to 10 days. The effect on onions is more pronounced than on garlic because onions are day-length sensitive, he explains. And onions planted toward the end of the planting window will suffer most in final bulb size.

To make a postemergent decision, he estimates weed pressure. If it looks like it would cost more than $500 per acre to clean up by hand-hoeing, he brings in the flamer.

In '95, he had 7 acres of yellow storage onions at the two- to three-leaf stage. Threatening were lambsquarters, pigweed and malva (dwarf mallow) as cotyledons and 1-inch rosettes. 'Flaming knocked out a big portion of the weeds, saved me at least $500 in labor, and still gave me a good yield,' he recalls. 'I got as many onions as from a neighboring non-flamed field that had lower weed pressure.'

Flaming garlic may take two passes - one preemerge and a second, if needed, by the time the tallest plants hit the three-leaf stage. Foster's garlic emerges more variably than his onions. This means 20 percent of the plants may be at the one-leaf stage while the most mature plants have three. The leaves are most likely to burn back, but they will regrow, he says.

Foster has increased flaming field speed over the years to 3.5 to 4.5 mph, using 10 to 15 gallons of propane per acre. At $0.90 per gallon, that's $9 to $14.50 per acre per pass for the fuel.

He removed hoods from the flamer when he added the second set of burners, but kept vertical side metal panels (that resemble cultivator crop shields) mounted on adjustable standards. 'You could put on a top hood, but I like to see the burners during operation.'

Shields keep the flames from being directed away from weeds by stiff breezes that are common during the afternoon 'prime kill time' of maximum air temperature and dew-free weeds.

Foster finds that transplanting more than pays for its extra field labor and greenhouse costs, thanks to full season savings in managing weeds and insects. The stronger, older plants are better able to fend off both types of pests. He transplants such crops as lettuce and cabbage, as well as crops with especially expensive seed such as hybrid pepper, hybrid cabbage and seedless watermelon. He cultivates transplants as soon as they are well-rooted enough to withstand a gentle wave of soil pushed in by sweeps from between the rows to smother in-row weeds.

Where soil is loose and flows well, a mechanically guided cultivator and straight rows give him good enough control to cultivate with only a 3-inch band for the row. A farm-fabricated guidance sled holds the 8-foot toolbar in place. The V-shaped structure of angle iron rides in a single furrow between the two or four beds being worked, locking the cultivator in alignment. Foster loosens sway bars on flat fields so the tool can easily follow the guide, but tightens them up on slopes where the mass of the sled may pull downhill.

His four-row bed shaper makes it possible to use either his two-row or four-row cultivators, both with sled guidance. He covers 0.66 to 1 acre per hour with the two-row unit and about 2.5 acres per hour with the four-row.

His onion cultivator is a farm-fabricated model with bed-top vegetable knives running along the outside edge of the outside rows. Five-inch-wide duckfoot sweeps cover the inter-row areas. He runs these tools within 1.5 inches of the onions where soil is friable and clod-free, a condition he attributes at least in part to his regular addition of compost.

His in-row, paired Texas-style rod weeders (torsion bar weeder) let him lightly disturb loose soil even closer to plants. The thin, round coil-mounted rods angle down from each side to almost meet tip-to-tip near the base of the crop.

His best success with a Lilliston rolling cultivator has been in sweet corn. He cultivates as soon as the crop is 3 to 4 inches tall, running slowly and with the curved tooth spider gangs set at a slight angle away from the rows. When the corn hits 10 inches tall, Foster pivots the spider gangs strongly the other direction to throw soil between the rows then travels at 4 mph or more.

In addition to their bed-top cleaning role, vegetable knives are his main tool for managing weeds in the wide inter-row areas in melon and squash plantings early in the season until vines shade the soil. He uses the knives and disk hillers to get close to plants and slice off weeds in the early season pass. The next weed flush is extinguished when he splits the vacant bed left between each planted bed. Shovels and disks push soil in both directions, creating 80-inch beds and smothering weeds along the outside edges of the planted beds.

When the vine crops begin to set runners, he makes a final pass with 12-inch top knives running as close as he can to the spreading plants. These long, bevelled straight knives run at right angles to the row just below the soil surface. He can offset about 6 inches of these knives in from the side and under the ends of the vines. The fast-spreading foliage takes over the weeding job after that.

When Foster has to cope with perennials such as morning-glory and Canada thistles in his long-season crops, he relies on cultivating with disks and knives for the sprouts up to 4 inches tall. After that size, the toughness of the plant prevents a clean kill, and handweeding becomes necessary. His goal is to prevent viable seed or root-mass from increasing the weed's threat to the field's next crops.