Horticultural Crops: The Farmers

Grower Shuts Off Weed Windows Before, After and Between Crops

Tom Harlow
Westminster, Vermont

  • 50 acres in crop rotation
  • soils: sandy river bottom, gravelly clay
  • fresh market vegetables, mostly wholesale
  • certified organic sweet corn, winter squash, short- and long-season greens, carrots, parsnips

Weed management highlights

Strategies: stale seedbed... specialized cultivation... crop rotation... handweeding... winter cover crops

Tools: tandem disk... mid-mount cultivator... offset cultivator tractor... basket weeder... in-row finger weeder... flamer... field cultivator... rolling cultivator

Detailed employee timesheets tell Tom Harlow exactly what it costs to produce each of his fresh vegetable crops each year. He drops the crops that don't pay, but says that harvest labor - not his steel-based weed management system - is usually the culprit.

He watches income closely from his high-labor root crops of parsnips and carrots. He wants to make sure that organic premiums balance out the timely, precision cultivation and hand-weeding costs that may hit $2,000 per acre. After eight years of fulfilling cropping standards to be a certified organic farmer, he's satisfied with his weed management system. 'Sure I'm fine tuning things, but it's close to being just where I want it.'

The weed species shift during his nine years of organic weed management bears him out. His annual tillage has fully suppressed perennials (troublesome witchgrass and sedges are gone), but opened up the niches for annuals such as chickweed and galinsoga. By matching competitive crops with weed pressure and rotating crops and tillage, he keeps these new opportunistic annuals - as well as the ever-present pigweed and lambsquarters - in check.

To build soil and keep winter-annual weeds contained, he plants winter covers of winter rye, or rye mixed with hairy vetch. He rotates greens, root crops, sweet corn or squash - with winter cover crops between each - then two to three years of red clover, sometimes harvested as hay and sometimes just clipped. This rotation mixes the type of crop root growth (shallow tap roots of greens, slender tuber of parsnips, radiating feeders of corn, and deep fibrous roots of clover) to prevent any weed species from developing a comfortable niche.

Harlow incorporates rye two ways. He uses a tandem disk with 22-inch blades on the fields he turns under earliest in the season, starting in late April. Later in the season, he uses a moldboard plow to handle more biomass from taller rye. His river bottom soils are not erosion prone, and the tillage improves their aeration and water infiltration. Until the fields are bedded, he kills weeds before they are an inch tall with brisk broadcast passes of his tandem disk or a field cultivator with barely overlapping 6-inch sweeps.

Next he forms beds that are 42 inches on center, elevated 3 inches higher than the 9-inch furrows between them. These become his 'stale seedbed' sites where he works to deplete the weed seed bank in the top few inches of soil. He sacrifices the soil-building value of several weeks of cover crop growth to provide time for two or three cycles of weed growth.

Harlow fabricated a bed-top, spiral rolling harrow that uproots and disturbs weeds. He cut the high-speed tool from a spiral basket roller section of a large field cultivator, then fashioned a bracket so he could belly mount it on his John Deere HC900. He says the high clearance, offset tractor is perfect for his cultivating jobs. Visibility is excellent, the machine is maneuverable and it takes him only 10 minutes to change cultivators. Even if he didn't also use it to spray and sidedress fertilizers and flame weed, he believes it would still be worth 'twice what I paid for it.'

For the final weed-killing pass at the last possible moment before crop emergence (for direct-seeded crops) or transplanting, he uses a German LP gas bed flamer. Its shrouded burner manifold (roughly resembling a rectangular rotary mower housing) concentrates heat on the soil surface. Its fixed 40-inch width and burner positions limit the tool's use to 'broadcast flaming' in a stale bed application.

The unit's six burners burn up $32 of LP gas per acre. Ground speed - and consequently, fuel use - -varies with conditions. Harlow travels about 6 mph on dry afternoons when weeds die more easily, but only 4 mph when he has to flame on dewy mornings. Harlow says his next flamer will be a standard U.S. toolbar version with targetable burners. He wants it to do broadcast flaming on beds of different widths, as well as banded flaming between rows of growing crops.

He plants most crops in two rows, each 9 inches from the bed center. Corn and collards go in 36-inch rows, and he direct seeds winter squash in rows 8 feet on center.

His most difficult weed challenge comes from his 2 acres of parsnips, a notoriously slow germinating crop. They take two to three weeks to come up and demand 100 growing days to produce their sweet white roots. His earliest planting requires that he compress his stale seedbed treatment, and the cool soils lengthen the time before the developing crop becomes competitive. The third planting in mid-July faces intense weed pressure at a time when labor for cultivation and hand weeding competes with early harvest of other crops. Harlow says he usually loses a fraction of the plantings to weeds but still turns a profit thanks to strong consumer demand and the unwillingness of other local growers to battle weeds in the crop as tenaciously as he does.

His root-crop strategy calls for a whole-bed flaming just as the earliest parsnips or carrots come through. When the crop has emerged and white-root weeds start to gain some color - and even reach up to a 2 inches height - Harlow runs through with a Basket Weeder (Buddingh Model H) within 1 inch of the row on either side. Its ground-driven heavy wire tined baskets roll horizontally against the soil surface to push through the soil and leave a mulch between the rows. No soil is thrown onto the weak parsnip seedlings.

Site selection to avoid patches of crabgrass is critical in turnips. With their growing centers well-rooted below ground, crabgrass plants survive scorched leaves from flaming and aren't killed by the shallow basket attack.

The next tools to protect the parsnips are the shanks of a belly-mount cultivator. Soil and weed conditions determine what soil-engaging tools Harlow mounts on the fixed vertical shanks. Shovels only 2 inches wide go deep when soil's been packed. Half-sweeps travel close to the row without moving soil toward it. These pieces have a sweep arm on only one side. They are usually mounted to extend into the middle row. Full sweeps 6 or 8 inches wide work the middles between rows and may throw soil in-row, depending on speed, proximity to the row and sweep profile.

After the first sweep cultivation, a hand-hoe pass removes all weeds in the parsnip patch, Harlow reports. He will usually do another sweep cultivation before parsnip tops fill out to suppress new weed growth. He pursues the later escaped weeds as time permits - even after the point that they could lower production - because of their economic impact if they plug his root crop harvester.

Two treatments with the baskets is often all he needs to manage weeds in lettuce. The crop has a short window, usually about 60 days from transplanting to harvest. Ideally, the lettuce field is disked immediately after harvest to prevent weeds from going to seed. Consistent, timely post-harvest cultivation is one of his greatest opportunities for improving whole-farm weed management, Harlow believes. He recognizes a second weed-seed reduction strategy would be more intensive composting of the cattle manure he applies each fall.

He reserves his in-row finger weeder (Buddingh Model C) for firm-rooted plants. Flexible rubber fingers 4 inches long radiating from a metal hub scuffle the soil surface right in the row, uprooting small weeds but moving around crops. The tool depends on the resistance of well-established crop plants to work when fingers are set to virtually overlap for total in-row weeding.

Harlow limits the tool to early plantings of corn (spike stage) and well-rooted cole crop transplants such as collards. Shallow-rooted crops - such as lettuce - can't stand to be fingered even if they are well-developed, he's found. And later corn could suffer damage to side roots close to the surface. To determine whether a transplant is ready for finger weeding, he employs the 'yank test' rather than count days in the soil. 'If it can stay in the soil when I give it a certain tug,' he's found, 'the weeder won't bother it.'

Where crop stalks are large enough to tolerate soil flowing against them, Harlow likes to use his Lilliston rolling cultivator. He leaves the spider gangs on his two-row model at the same angle to the row for both early and late passes. Speed makes the difference. He goes through first at 2.5 to 3 mph, doing his best to throw about 1.5 inches of soil at the base of 2-inch corn plants. ('In reality, some don't get anything and others get buried. You have to watch.') About 10 days to two weeks later, a trip through at 5 mph throws up 8-inch hills to smother all weeds and anchor the plants against wind lodging and picking stress. Earlier plantings of corn develop more slowly, and usually require more frequent cultivations than do later, more competitive plantings.

The rolling cultivator works well for first cultivation in potatoes to begin the hilling process, and for collard greens if they jump off to a strong start. In '96, he did no hand weeding on the robust leaf crop until first harvest, thanks to timely cultivation and quick canopy development. Workers hand-pulled mature weeds and weeds that interfered with the five pickings of tender leaves as the crop matured.

To manage the areas between his widely spaced rows of squash, Harlow uses his field cultivator whenever weeds get to be 1 inch tall. He removes the center shanks so he can straddle the crop rows. When he can no longer drive over the bushy plants, he makes a hand-hoeing pass to remove weed pests and thin the crop. Just before the runners extend to close the row middles, he tills the area with a final broadcast pass of the (fully tooled) field cultivator.

His 'rescue unit' is a tractor-powered rotary tiller. It's his tool of choice to finely incorporate crop residue after harvest, and sometimes is called upon to knock down part of a crop field where weeds have the upper hand - before they go to seed and threaten future crops, as well.

Harlow is convinced that mechanical weeding is the most effective, cost-efficient way to keep crops clean for his system. If he weren't farming organically, he'd keep his same tools and most of the same crops. He says he'd let someone else grow the parsnips and carrots.