HOME | Safflower Contents | Diseases [12]

Insect Management

Many species of insects can be found in safflower fields. Some use safflower as a food source, but they only rarely affect yield. Safflower yields are based on the number of plants per acre, the number of viable flower heads per plant, the number of seeds per flower head, and to a lesser degree, the size of the seeds. Like wheat, barley, rye and oats, compensation among these diverse yield components is possible in safflower. Additionally, safflower plants can form additional buds if primary buds are damaged. Because compensation is possible, insect damage rarely influences yield in a significant way. In practice, wireworms and cutworms, which affect stand establishment, and lygus bugs, which migrate from safflower to cotton, are the only insects commonly controlled with pesticides in safflower (see below). Other insects are seen occasionally and are mentioned for completeness.

Insect damage to safflower can occur at crop establishment, during seedling and stem growth, and during the bud to flower stage. The most susceptible period likely is the bud to flower stage. Thrips and lygus bugs potentially are the most damaging pests. Bud removal experiments (simulating bud loss from insect damage) indicate that as late as full bloom, substantial bud loss can occur without significant loss of yield. Removal of more than 50% of the buds of the Gila variety (an older variety) by mechanical de-budding at the onset of bloom did not reduce yields in one experiment. Buds removed were younger and less than 1/4 inch in diameter, and most of the buds remaining after mechanical removal were close to blooming. Removing buds at this period reduced the number of good seed heads but the number of seeds in the remaining heads was nearly doubled, providing yield compensation. The seeds formed by debudded plants were similar in size to those from plants that were not debudded. Insecticides used to reduce bud loss from insect pests had no significant effect on yield. Most safflower varieties appear to react similarly to Gila. Insect pests have to occur at a high level over an extended period for crop loss to be measurable.

Planting safflower at a locally optimum time from the perspective of crop development and water use will usually allow the crop to develop vigorously enough to tolerate most insect damage. The use of insecticides against safflower pests generally is not required. In cotton growing regions of the state, however, safflower may be sprayed to control lygus bugs as the crop begins to mature, to prevent the migration of those insects to near-by cotton fields. This control is for the sake of the cotton, rather than the safflower (see below).

Insects observed in spring or at establishment

Cutworms (Agrotis spp.), are caterpillars that live below ground and cut off seedlings at or just below the soil line. Other species (Peridroma saucia and Euxoa auxiliaris) are nocturnal, feed above ground and may occasionally be encountered. Areas in fields may be barren of plants following cutworm feeding. Cutworms are encouraged by previous crops of alfalfa, small grain crops, and by grassy weeds. If sufficient plants are present, safflower can compensate for some seedling loss. If damage is severe, protection of seedlings with insecticides may be necessary. Carbaryl (Sevin) can be used as a bait after damage is observed. A bacterial insecticide: Bacillus thuringiensis also is available and may be used if seedlings are large enough to withstand moderate damage while the bacteria infests the insects digestive system (one to two days). For all pesticides, observe current label restrictions.

Wireworms, Limonius spp., occasionally attack plantings. They may reduce the numbers of plants by destroying some of the germinating seeds or by damaging roots. In a stand with sufficient plants, modest wireworm damage likely will not reduce yield significantly. If significant damage is anticipated, Isotox (Lindane) may be used as a seed treatment.

In research trials, seed corn maggot, Delia platura (Meigea) has damaged safflower stands in plots with especially high levels of cover crop residues and organic matter, conditions favoring the insect. Excessive moisture, or cool, wet periods slowing seedling growth and prolonging the plants' susceptible stage may lead to damage.

The green peach aphid, Myzus persicae (Sulzer), may become abundant enough in the spring to damage primary buds and seed heads, which develop a spotty or mottled yellow coloration, and seed production can be reduced by as much as one-third on individual plants that are severely affected. Vigorous crops usually compensate for loss to aphids, and they are rarely controlled.

Black bean aphids, Aphis fabae Scop., can develop high populations on leaves and terminals of single plants. Small to medium-sized groups of plants generally become infested near the margins of fields. As many as 1,200 or more aphids can develop on one plant and severely stunt or completely destroy it. More moderate infestations, about 500 aphids per plant, can still cause appreciable stunting. Light infestations, with less than 50 to 60 aphids per plant, can be tolerated. Individual plants, when severely infested, have lost on the average 50 to 75 per cent of the seed. Despite the losses from individual plants, control has usually been unnecessary because only small areas of the field tend to be affected. Labeled insecticides may be considered when large numbers of plants are moderately to severely infested, or a large number of aphid colonies are found throughout the field.

Onion thrips, Thrips tabaci Lind., are an occasional pest of minor or local importance. Silvering and bronzing of young safflower seedlings can occur when onion thrips emigrate in large numbers from newly harvested, nearby small grain fields. Infestation is brief and the damage minor. Control has not been necessary.

Insects affecting safflower during its vegetative and reproductive stages

Western flower thrips, (Frankliniella occidentalis Perg.) causes most of the early to midsummer browning, bronzing, and blasting of buds observed in safflower fields. Damage occurs on developing buds largely before bloom and before high populations of lygus bugs appear. Twenty to twenty-five thrips nymphs per bud can cause bud loss. When infestations average 150 nymphs or more per bud the nymphs can destroy all of the buds on a plant. Plants must lose approximately 40 per cent of their buds before a measurable loss of seed occurs. Insecticides are not recommended for the control of thrips until 25 to 30 per cent of the early buds are bronzed and blasted prior to the onset of bloom. Such high losses to thrips are rare.

Lygus bugs, (Lygus hesperus Knight), must be present in large numbers, 40 per sweep of a standard (15 inch diameter) insect net, to cause significant seed losses. They can cause a moderate degree of bud browning and blasting only when they feed in large numbers on the developing buds prior to bloom. Usually the damaged buds can be distinguished by their sickle shape from those injured and blasted by thrips. Most buds fed on by lygus bend over and turn brown, while buds browned and blasted by thrips remain upright. Lygus bugs usually cause economic damage (bud loss) only in late-sown fields, after high population densities have had time to develop on safflower or neighboring crops. Insecticides are not recommended until at least 25 to 30 lygus bugs (including nymphs) per sweep of a standard insect net are present before the primary buds begin to bloom.

Immature safflower buds damaged by lygus feeding.	Mature safflower buds damaged by lygus feeding.

Lygus bugs and flower thrips generally remain to feed on seed heads developed from the buds. However, most of this later injury is superficial, causes very little loss of seed heads, and only occasionally results in the loss of a few seeds. The head becomes too tough for more than localized injury. Insecticides are not required after seed heads develop from primary and secondary buds. The discolored or dirty appearance of seed heads that can develop and the prevalence of lygus bugs are misleading. If lygus must be controlled to prevent migration to cotton or other crops, labeled insecticides should be applied before lygus nymphs have developed wings. In the San Joaquin Valley, controls should be applied by the time 667 degree days (above 52° F base temperature) have accumulated after April 1, or after planting, whichever occurs first. Two organophosphate pesticides are currently available (dimethoate and methidathion), but their effectiveness against lygus has diminished in recent years. Labeling restrictions change rapidly, so growers should consult cooperative extension personnel or licensed pest control advisors before using a material.

Other types of insects occur occasionally in safflower and are included in Table 6.

Table 6. Insect and mite pests of safflower
Scientific name	Common name	Damage	Control threshold	Control
Agrotis spp.	Cutworm	Stand reduction	Control if damage is severe	Labeled pesticides
Aphis fabae Scop.	Black bean aphid	Stunting and death of plants	50 to 60 aphids per plant; large areas of the field affected	Labeled pesticides
Frankliniella occidentalis Perg.	Western flower thrips	Bronzing or blasting of flower buds	25 to 30 early buds bronzed or blasted prior to bloom	Labeled pesticides
Limonius spp.	Wireworm	Stand reduction	None	Seed treatment
Lygus hesperus Knight	Lygus bug	Bud browning and blasting	25 to 30 per sweep (standard insect net); 40 per sweep required for significant damage	Labeled pesticides
Melanoplus spp. Schistocera spp.	Grasshopper	Leaf chewing	None; may be severe on occasion, especially on field edges or under dry land conditions during drought	Labeled pesticides
Myzus persicae (Sulzer)	Green peach aphid	Damages or destroys primary seed head; may reduce crop yield by one-third	None	Labeled pesticides

Safflower Contents | Diseases [12]

HOME | About | Crops | Contacts | Publications

Modified: 10 Feb 2000 Comments to webmaster@agric.ucdavis.edu