UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY 4, CALIFORNIA CONTROL OF THE TOMATO MITE IN NORTHERN CALIFORNIA A. E. MICHELBACHER, 1 L. M. SMITH, 2 and GORDON L. SMITH* The tomato mite ( Phyllocoptes destructor ) , also called tomato russet mite, does serious in- jury to tomatoes in California. This leaflet gives the latest recommendations on control that are particularly applicable to northern California. The pest is a free-living, microscopic mite, which appears slightly humped and yellowish white under high magnification. It crawls about slowly on the surface of the stems and leaves of the tomato plant and sucks out the cell contents. The color of the stems and leaves then becomes greasy brown or russet. Injury may appear in June, but seldom becomes serious enough to be noted until late July and August. Starting on the stems near the ground, the infestation works up the plant and -gradually causes the lower leaves to become dry. In hot weather rapid de- foliation occurs, resulting in sunburned fruit. If the basal portions of tomato vines show a greasy bronze discoloration, while the outer growth still appears normal, mite damage should be suspected. The tomato mite reproduces from eggs and passes through many generations in a season. In the field continuous reproduction has been re- ported by Bailey and Keifer 4 from early May un- til frost. Host Range The tomato mite feeds and reproduces on a num- ber of solanaceous plants. Among the more fa- vored cultivated hosts are tomato, potato, and petunia. Wild hosts (less favored than these) include nightshades and daturas. Control Every effort should be made to keep this mite from establishing itself in tomato plantings. Assistant Entomologist in the Experiment Station. 2 Assistant Entomologist in the Experiment Station. Associate in the Experiment Station. ^Bailey, S. P., and H. Keifer. The to- mato russet mite, Phyllocoptes destructor Keifer: its present status. Jour. Econ. Ent. 36(5) : 706-12. Seedbeds should not be located near host plants of the pest. Petunias have been observed to be heavily infested with the mite during the winter; apparently this plant is a very favorable over- wintering host. Some varieties are more suscep- tible to the mite than others, but as a precau- tion none should be allowed to grow near seedbeds. Also, where possible, petunias and other host plants should be eliminated from areas surround- ing tomato fields. According to all the experimental work, dust- ing sulfur is the best insecticide for controlling the mite. Sulfur, however, has a deleterious ef- fect upon canned tomatoes and should be used with caution. The dusting program described below has been designed to reduce the sulfur hazard as much as possible. In the harvest season a dust con- taining more than 25 per cent sulfur should not be used without the consent of the canner who is purchasing the tomatoes. In areas where the mite is likely to be injuri- ous, it has been found desirable to apply straight dusting sulfur to the tomato plants sometime be- tween June 15 and July 15. Undiluted sulfur dusts can be safely used at this time because in most regions the tomato vines are just beginning to set fruit. The amount of dust needed varies with the size of the plants, but will be 10 to 25 pounds per acre. Good control depends upon even- ness and thoroughness of application. Occasion- ally worms threaten damage during, this period; insecticidal dusts for their control should not contain over 50 per cent sulfur. If the tomato mite is thoroughly held in check through July, later applications of dusts need not contain more than 25 per cent sulfur. Dusting at 3- to 4-week intervals should be sufficient to hold the pest in check. Usually by mid-September, danger of serious mite damage is greatly lessened by cooler weather conditions; . after that time, if mite in- jury is not apparent, sulfur can be omitted from the dusts used for worm control. If control was not obtained or was neglected early in the season, and the tomato mite shows up in August or later, the localized spots of infes- tation probably should be treated with straight dusting sulfur. If a field is kept under close observation, these islands of infestation can be detected while they consist of only a few vines, and treated promptly by means of a hand-duster. [1] The rest of the field should have an application containing not more than 25 per cent sulfur. If a dust of higher sulfur content is used (and this may be desirable) the grower should first obtain permission from the canner who holds the tomatoes under contract, before applying it. An insecti- cide containing 25 per cent sulfur should be used for the later dustings. In most sections of the state, ordinary dusting sulfur has proved effective against the tomato mite. In cool areas near the coast of southern California, however, the United States Depart- ment of Agriculture, Bureau of Entomology and Plant Quarantine, has obtained better results with finely divided dusting sulfur than with the ordinary product. The choice of a material for use along with the dusting sulfur depends upon the kind of worms to be controlled. Where the tomato pin- worm is a pest, cryolite is the proper insecti- cide. Pinworm damage is most likely to occur in southern California and the southern San Joaquin Valley. Elsewhere in the state calcium arsenate is probably the best insecticide to use in con- junction with sulfur. This material is very ef- fective against all the more important worms attacking tomato, except the tomato pinworms. If worms are not a problem, the carrier for the sulfur can be talc or a similar material. Where a cryolite -sulfur dust is used, the amount of material employed per acre ranges from 20 to 40 pounds, depending upon the size of the plants. For the calcium arsenate and sulfur combination, 20 to 35 pounds should be used per application. Although the tomato mite is a serious pest, the grower should remember that worms also can do much damage. Unless they are controlled, losses as great as might have been caused by the tomato mite are likely to occur. Where tomatoes are being grown for the fresh market, undiluted dusting sulfur can be applied at any time with- out danger of a sulfur-residue problem. If, however, any of the tomatoes are to be canned, the problem of sulfur removal should be consid- ered. Poisonous Residue The insecticides recommended for worm control are poisonous. Cannery washers are able to re- move this poisonous residue effectively. Toma- toes intended to be eaten fresh should be washed or carefully wiped free of any residue before being used or marketed. [2] 5m-4,'U(90;