NEWSLETTER ARTICLES

Vegetables and Plant Pathology


From our Central Coast Agriculture Highlights newsletter June 1997 issue:

SEED GERMINATION AND SOIL TEMPERATURES
by Franklin Laemmlen


Rapid seed germination is important to good stand establishment. The longer the seed spends in the ground, the greater the chances are that insects, disease organisms, nematodes, or adverse moisture conditions will cause damage or disrupt the germination and emergence process.

If moisture is adequate, soil temperature is the second critical physical factor in seed germination. Note that sprinkler irrigation has a cooling effect and will suppress soil temperatures several degrees. The following chart lists days to seedling emergence for several crops commonly grown on the Central Coast. Generally, temperatures between 65º and 85ºF are most ideal for most crops. When soil temperatures drop below 65ºF, except for lettuce, emergence time increases to the point where transplanting becomes a desirable option.

SOIL TEMPERATURE AND PLANT EMERGENCE (DAYS)
SOIL TEMPERATURE DEGREES F

CROP50o59o68o77o86o
Asparagus5324151012
Beans (snap)NG161186
Cabbage159654
Carrot1710766
Cauliflower2010655
Celery16127NGNG
Lettuce74323
Onions137544
Parsley2917141312
Peas149866
PepperNG251388
Spinach127656
Tomato4314866
NG=no germination
Source: Knott's Handbook for Vegetable Growers




PLANT DISEASE DIAGNOSTICS AND SOIL TESTING LABS IN CALIFORNIA
by Franklin Laemmlen


The following is a list of laboratories, which were/are active in plant- and soil-testing as of April 1997. I suggest you call the laboratory prior to submitting samples. Quite often samples must be taken, packaged and sent in a particular manner in order to obtain the best possible diagnosis. The laboratory can provide you with these instructions. Finally, no laboratory has been intentionally omitted from this list. However, it is hard to keep track of everyone. If you operate a laboratory, which processes commercial plant and soil samples, and you wish to be included on a future list, please contact our office at 805/934-6240.

PLANT DISEASE DIAGNOSTICS AND SOIL TESTING LABS IN CALIFORNIA
Laboratory Name
Phone
Address
Services Offered
A&L Laboratory209/529-40801010 Carver Road, Modesto, CA 95350plant, soils, compost nutrient testing; no diagnostics
ATS Laboratories (Ag Tech Serv)619/344-2532106 So.8th St., Brawley, CA 92227soil, plant, water NPK tissue analyses
Agri Service (Mary Matava)619/727-54512142 "B" Industrial Ct., Vista, CA 92083test citrus and avocado for Phytophthora
Associated Labs (Ed Behare)714/771-6900806 N.Batavia, Orange, CA 92668plant & soil tests, incl.NPK, heavy metals, ag. suitability
Butler's Mill Lab619/263-61815180 Naranja St., P.O.Box 740069, San Diego, CAsoil NPK testing
Crop Doctor Lab (Heather Vallier)805/962-0505or 805/927-77072751 Ernest Place, Cambria, CA 93428turf, ornamentals, trees, veg.crops diagnostics
Fallbrook Ag Lab Inc. (Carolyn Wells)619/728-4828433 S.Main St., Fallbrook, CA 92028ornamental plant diagnostics
Fruit Growers Lab, Inc.-FGL805/659-0910P.O.Box 272, Santa Paula, CA 93060soil, tissue&compost testing; Phytophthora, nematodes
Gary King, Horticultural Consultant619/941-74091321 Hodges Rd., Oceanside, CA 92056agricultural&horticultural crop diagnostics
Orange County Dept.of Agriculture (Richard Tiffer)714/447-7100Orange Cty.Dept.of Agriculture, 1010 S.Harbor Blvd., Anaheim, CA 92805plant disease diagnostics
PACE Turfgrass Research (Larry Stowell)619/272-98971267 Diamond St., San Diego, CA 92109turf diagnostics
Pacific Plant Health (Don Ferrin)909/342-02241485 Spruce St., Ste.D, riverside, CA 92507plant disease diagnostics
Perry Laboratory408/722-7606471 Airport Blvd., Watsonville, CA 95076horticultural advising & testing
Plant Disease Diagnosis (Louellen Pierce)510/937-3841780 Palmer Rd., Walnut Creek, CA 94596turfgrass and plant disease diagnostics
Primus Group, Inc.805/922-00553130 Skyway Dr., Ste.308, Santa Maria, CA 93455pesticide residues, microbes, plant tissues, soil and water
San Bernardino County Dept. of Agriculture (Rod Lampman)909/387-2123San Bernardino County Dept. of Ag., 777 E. Rialto Ave., San Bernardino, CA 92415plant disease diagnostics
San Diego County Dept.of Agriculture (Pat Nolan)619/694-2753San Diego County of Ag., 5555 Overland Ave., Bldg.#3, San Diego, CA 92123plant disease diagnostics
Soil and Plant Laboratory, Inc.714/282-87771594 North Main St., Orange, CA 92867diagnostics, soil, plant nutrient analyses
Tree Associates (John Lichter)916/795-15173963 Central Lane, Winters, CA 95694tree and landscape problem diagnostics (N. Sacr. Valley)
Wallace Laboratories800/473-3699365 Coral Circle, El Segundo, CA 92045plant, soil, compost analyses, no diagnostics
Compiled by Marcella E. Grebus, Ph.D., Plant Pathology Specialist, UC Riverside.



TIPS TO PREVENT KARNAL BUNT CONTAMINATION OF GRAIN AT HARVEST
by Franklin Laemmlen


Concern about Karnal bunt in wheat should still be on the mind of every grain producer this harvest season. If your fields are clean, you should make every effort to prevent contamination at harvest. If you have fields with the disease, you should take precautions not to spread it to clean fields or to your neighbors. Several strategies may be used to reduce the possibility of Karnal bunt contamination in the harvested grain. These strategies have not been studied scientifically but are based on common sense and experience with last year’s harvest. These strategies assume that harvesting equipment can spread Karnal bunt spores, that Karnal bunt is more likely in certain fields or parts of fields, and that the soil contains spores which can contaminate the grain.

A. Be aware of the possibility of introducing spores with harvesting equipment:
    1. Clean combines before entering fields of new customers. This procedure may include removing crop debris from accessible areas on the combine, running the combine to clear out grain and straw, and using a high pressure air hose to blow off dust and remaining debris.
    2. Sweep loose grain out of trucks between customers.
    3. Properly adjusted combine with adequate air flow can help clean surface contamination off the grain.
B. Harvest fields more likely to have Karnal bunt last or separately. This includes:
    4. Fields of bread wheat which are more susceptible to Karnal bunt than durum.
    5. Fields that received rain or heavy dew between late boot and 2 weeks after heading when wheat is most susceptible to the disease.
    6. Fields where wheat was grown two or more seasons consecutively during the past five years.
    7. Fields with excessive vegetative growth.
    8. Fields with a high population of weeds, particularly where pasture grasses have been grown in the past.
    9. Fields irrigated with overhead sprinklers.
C. Harvest certain parts of the field separately.
    10. The combine may pick up soil contaminated with spores when cutting around the edges of the field or along the border ridges. The edges of the field may also contain more dust than the interior due to trapping of dust from nearby roads and adjacent fields.
    11. The ends of fields may be more susceptible to Karnal bunt if water ponding is frequent in these areas.
    12. The header may pick up soil when harvesting lodged wheat.
Information adapted from article written by Mike Ottman, Extension Agronomist, University of Arizona.



ROOT MAGGOT PROBLEMS
by Franklin Laemmlen

With the increasing use of minimum tillage, which leaves much plant debris on and near the soil surface, it appears that the incidence of root maggot problems in newly transplanted and emerging seedlings is also becoming more prevalent. Seedcorn maggot is a common cause of seedling damage, but other root maggots may also be found. The following information should help with identification and management.

Seedcorn maggot injures plants and stands by feeding on sprouting seeds or seedlings. They attack beans, cole crops, corn, curcurbits, onions, peas, potato seed pieces, radish, spinach, and turnips. The maggots burrow into the seed, feed on its contents and often only leave a hollow shell. They also allow disease organisms to enter and rot the seed. In transplants they will invade the plug, feeding on the larger roots and stem of the seedling. The result is stunting and wilting of the young plants. Extensive feeding and burrowing results in death.

The cabbage maggot is a specialist on cole crops and cruciferous root crops. It can also develop on weeds and wild plants in the crucifer family. The larvae feed on the underground stems, causing stunting and wilting. Occasionally, they will enter the heads of Napa cabbage and can be extremely troublesome on turnips by their tunneling in the bulbs. Seedcorn maggot has also been identified in the Santa Maria and Edna Valley area in Napa cabbage. The feeding activity produces a tattered leaf injury inside the Napa head. The maggots also often introduce bacteria which initiate a soft rot in the heads.

Onion maggots infest onions, leeks, shallots, garlic, and chives. The larvae bore into the underground stems and consume the interior of bulbs, reducing stands and decreasing uniformity. Plant mortality may also occur, plus internal soft rotting of infested bulbs.

Decaying vegetation (i.e., covercrops and crop residues) at planting attracts the adult flies of all these maggots. Female flies live approximately six weeks and lay their eggs at the base of the host plant or on the soil. They produce an average of 270 eggs. The adults are abundant all year long, however, seedcorn maggot damage is most severe in the early spring when the weather is cool and the soils are wet. Cabbage maggots can cause damage all summer long.

Eggs hatch in one to nine days, depending on the soil temperature. Larvae develop rapidly with warm temperatures. Within one to three weeks mature maggots pupate. Adult flies emerge approximately one to three weeks later.

Prevention is the best management strategy. Disc previous crop residues into the soil at least two weeks prior to planting (a longer period of decomposition may be necessary in cooler weather). This allows the maggots to mature and pupate. When rotating into a field with crop residues cannot be avoided, it is best to treat with a commercial seed protectant insecticide. Organic growers can cover the field with floating row cover to exclude the adults of cabbage maggots. However, seedcorn maggots, because of their varied diet, may already be present in the soil and can attack seeds under floating row covers. The adult flies may travel several miles to find a suitable host. They are also attracted to recently tilled soil and are stimulated to lay eggs in soil with decaying organic matter. Insecticides recommended for root maggot control include diazinon, chlorpyrifos, and lindane. These materials may be applied as seed treatments, in furrow sprays or granules, or broadcast sprays or granules which are incorporated preplant. Check chemical labels against the proposed use to determine which chemical can be used in your situation.

Information partially obtained from Row Crop Reporter, San Benito County.