Summary of Cauliflower Trials and Recommendations

1. Varieties.
Winter cauliflower varieties require a cold period to induce head formation. The heads, or curd, of overwintering cauliflower are composed of true flower buds and are usually of lower density than for Snowball types in which the curd is floral primordia tissue. Stems often tend to be slightly green and flavor tends to be mild. Because of the low density and tendency to break up when the stem is removed, these varieties are considered more promising for fresh market than for processing.

Four variety trials were conducted over five years. Very early varieties which mature in March are not acceptable for commercial production in the Willamette Valley. They must be planted early to achieve acceptable head size. Early planting increases the risk of curd formation during winter warm spells, increasing the probability of winter damage, and reduces the time available for growing another crop in the season before planting the cauliflower. Early curd formation greatly increases the risk of crop loss since the curd cannot stand severe or extended freezing temperatures. The earliest variety which has consistently proven adapted to the Valley is Armado April, although Armado Quick and Preminda have produced well in mild winters.

Varieties which mature in late May or June have also not done well in these trials. The curd is often discolored and loose, and curd texture of the latest varieties often becomes fuzzy or ricey. Tieing heads might prevent discoloration, but even well-protected heads have had poor curd quality. Insect problems also increase with the warmer weather.

The best varieties have been those which mature in early April to mid-May in most years. A range of three or four varieties should cover this period. A list of recommended varieties is found in Table 24.

Table 24. Recommended overwinter cauliflower varieties for the Willamette Valley.                   Maturity   Yield potential   Comments                                 Armado April    1 April    medium           Good color, best early variety  Inca            7 April    medium           White curd, domed head, may need tieing  Marchpast       7 April    medium           High quality  Aprilex        20 April    med. high        Good curd quality  Armado May     20 April    med. high        Tends to have leaves in head  Markanta       20 April    medium           Variable, excellent in some trials  Arminda         1 May      high             Color good if tied  Armado Tardo    5 May      medium           May discolor in warm weather  Armado Clio    10 May	   med. high        May discolor in warm weather  Maya           10 May      high             Best late variety                          

2. Planting window

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Except for the very early varieties, planting date has little effect on maturity. The latest practical direct-seeding and transplanting dates are August 10 and September 10, respectively. The recommended earliest dates are July 20 for direct-seeding and August 20 for transplanting. Both very early and very late plantings are more susceptible to winter injury. For late maturing varieties which do not form a curd until the danger of hard freezes has passed, seeding in early July or transplanting in early August is feasible. In the mild winter climates of England and Holland, seeding is often in June. With the warmer summers of the Willamette Valley, such early seedings are unnecessary as adequate growth can occur before the onset of cold weather. Such early plantings eliminate double cropping in the year the crop is planted and increase risk of freeze damage to the cauliflower.

3. Planting site.
The soil type must be a well-drained sandy or silt loam without low spots which collect standing water in the winter. The site should be sheltered from the cold, desiccating winds which occasionally invade the Valley from the north and east. Frost pockets should be avoided; good air drainage is essential. Winterkill temperatures are from 0° to 15°F, depending on duration of the low temperature, soil moisture, wind velocity, relative humidity, variety, and stage of growth. Some loss of yield and quality can be expected when the temperature reaches the low teens.

4. Fertilization.
Soil pH should be adjusted to at least 6.0 with a mixture of calcitic and dolomitic limes. The initial fertilizer application should include 60 to 80 pounds N/acre unless the cauliflower follows a heavily fertilized crop with residual soil nitrogen. Chicken manure is often used at a rate of 10 tons/acre for the initial N application. Phosphorus and potassium should be applied in accordance with soil test. Ranges for application of these nutrients are given in Table 25. Cauliflower has a high sulfur requirement and Willamette Valley soils are often S deficient. Sulfur should be applied before planting. A second application may be desirable after a very wet winter.

The bulk of the N application should be made in late winter and spring, 150 to 200 pounds N/acre, split between two or three applications. Nitrogen source trials indicated a possible advantage to applying N in the NH4 form; however, acid-forming fertilizers such as ammonium sulfate and ammonium nitrate should not be used if soil pH is below 6.0.

Magnesium, calcium, boron, molybdenum, copper, and zinc are other elements likely to be limiting for cauliflower production. Magnesium is routinely applied to spring-seeded cauliflower as dolomite or Epsom salts and the same requirement exists for the overwinter crop. Rates of up to 20 pounds Mg/acre should be based on soil test. Calcium is not likely to be deficient on properly limed soils. Boron is usually deficient in Willamette Valley soils. Up to 5 pounds B/acre may be applied before planting or as a spring foliar spray, based on soil test. Molybdenum deficiency is common in cauliflower and may be prevented by application of 1 pound Mo/acre as ammonium or sodium molybdate, usually incorporated with the pre-plant fertilizer. The seed may also be treated by dissolving 0.5 ounces sodium molybdate in 1 ounce of water and mixing with enough seed to plant 1 acre. Copper and Zn should be applied only if a soil test indicates a deficiency.

Table 25. Overwintered cauliflower fertilizer requirements (pounds/acre)                  N        P205      K20      S       Mg      Mo       B  At planting:   0-80     70-150   30-150    30     0-20    0-1      2-4  In spring:   150-200      0        0      0-30     0       0        0     Rates of K20, Mg, Mo, and B should be based on soil test.  

5. Cultural practices

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Seedbed or transplant bed preparation is the same for the summer crop and fall crop. If direct-seeding, 5-6 ounces of seed/acre are necessary to achieve a seedling density of about 3/foot. After thinning, plant spacing should be 18 inches in the row and 36 or 40 inches between rows. Seed should be planted 1/2 to 3/4-inch deep with a precision seeder. Transplanting offers several advantages, including more possibilities for the crop preceding the cauliflower, avoidance of seedling stand establishment problems, and less insect and weed problems. Cultivation, after thinning to control weeds and loosen the soil, is a good practice. Both direct-seeded and transplanted crops require irrigation until the start of the fall rains.

6. Pest control.
The major pest problems include cabbage maggot, slugs, head maggots, cruciferous weeds (mustard family), and grasses. Chlorpyrifos and fonofos have provided acceptable control of cabbage maggot and symphilids and many slug baits are available. Local Cooperative Extension offices or licensed pesticide consultants should be contacted for current pesticide registrations. The weed control program includes an incorporated application of trifluralin before planting, followed by cultivation, and an application of napropamide after thinning. Consult the herbicide labels for appropriate rates. Good weed control is essential. Diseases commonly encountered include mildew, blackleg, black rot, and root rot. Control methods are the same for the summer crop and fall crop.

7. Rotations.
Overwintered cauliflower can follow any crop which matures sufficiently early and which does not result in residues of herbicides or other pesticides not registered for cauliflower. Ideal candidates include peas, early beans, overwintered onions, leafy greens, early root crops, and winter wheat. Overwintered cauliflower should not follow a badly shattered grain crop, as thick stands of volunteer grain will seriously compete with the crop. Fields should not be in cole crops in successive years and those infested with cruciferous weeds or clubroot must be avoided.

Most row crops can easily follow overwintered cauliflower because of the early harvest season and lack of herbicide residue problems. The cauliflower should not be followed with another cole crop. Fertilizer needs may be reduced as residual N should be available to the following crop.

8. Risks and rewards.
The greatest risk is the possibility of losing the crop to a severe freeze. The recommended varieties have all survived temperatures as low as 10°F, but head size and quality can be reduced at this temperature. Marketable crops should be produced in 4 of 5 years.

Markets are hard to predict. During April and May the major competition is from central and southern California growing areas that are able to produce quality fall-type varieties in the spring.

Fertilizer requirements are also higher for overwintered cauliflower than for spring-planted cauliflower since N and other elements leached by winter rainfall must be replaced in the spring. However, application of most of the N can be delayed until the extent of winterkill has been determined.

Among the advantages to the crop are reduced costs for irrigation, the lack of insect pests such as moth larvae and loopers, a cash flow during a period when crops are not usually harvested, and the potential for three crops in two years. Marketable yields of 500 cartons or 4,500 heads/acre are not uncommon.

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