CONTROLLING THE TUSSOCK MOTH

PAUL H. ROBERTS, JAMES C. EVENDEN.

In the field headquarters at Moscow, Idaho, a tense group of men were waiting for the signal that was to start the greatest of all airplane offensives against an insect. It was 3 o'clock on the morning of May 22, 1947. The sun had not yet limned the mountain majesty of northern Idaho and neighboring Washington or the desolation wrought in the forests by the tussock moth. The report came: Weather clear; wind velocity 5 miles an hour. It was relayed to the Laird Park airstrip and the municipal airport at Moscow, the seat of the University of Idaho, and nearby Pullman, the seat of Washington State College.

At 3:20 a. m. the big C-47 trundled onto the runway, roared through a short take-off, then rose and turned toward the rough terrain of Moscow Mountain to spread 1,000 gallons of DDT spray over 1,000 acres of infested fir timber. The Ford trimotors followed. Simultaneously the small planes at the Laird Park airstrip went out, one at a time.

They were after the Douglas-fir tussock moth (Hemerocampa pseudotsugata McD.) , which early in 1946 appeared in epidemic proportions throughout a large forest area near Moscow, Idaho. A native of northwestern United States and southeastern Canada, the small insect can kill its preferred hosts, Douglas-fir and the true firs, in a year if it destroys all the foliage; partial defoliation may result in serious top killing and the death of trees if it continues for several years.

In its life cycle this insect produces but one generation each year. Eggs are laid in August and September and hatch the following spring in late May. The tiny caterpillars are active and will travel relatively long distances in search of food. They become full-grown by late August, pupate, and transform to new adults in about 2 weeks. As the female moths are wingless, eggs are usually laid on or near the pupal case from which the moths have emerged. Any widespread distribution of an infestation must be by means other than the flight of adult moths. It is known that the young, hairy caterpillars are carried long distances by air currents. When disturbed, they drop from the limbs and hang suspended on a fine silken thread often 5 feet or more in length, which they spin as they fall. This thread and the body hairs of the caterpillar offer considerable wind resistance, and air currents of about 10 miles an hour will carry them away.

By early summer of 1946 whole mountainsides appeared brown from defoliation of trees by the insect. In the Idaho territory these brown areas intensified public concern as to remedies. On July 15 the Moscow Chamber of Commerce called a meeting for a discussion of the situation. Owners of timberland, private citizens, and representatives of lumber companies, the Idaho State Forestry Department, University of Idaho, the State Extension Service, the Forest Service, and the Bureau of Entomology and Plant Quarantine attended. They decided that it was too late to attempt control action in 1946 and that a survey should be made of the situation by the Forest Service and Bureau of Entomology and Plant Quarantine.

The two agencies gave a joint report at the annual meeting of the North Idaho Chamber of Commerce in Moscow on November 21. The primary facts disclosed were: (1) Within a gross area of about 500,000 acres, 350,000 acres with an estimated stand of 1,518,000 thousand board feet of the Douglas-fir and white fir timber were infested and an additional 1,182,000 thousand board feet were threatened; (2) the economic values involved (including, but not limited to, stumpage, lumber, pay rolls, and taxes) were more than 100 million dollars; (3) aerial spraying with a DDT solution was the only feasible means of control on the rugged terrain; (4) the estimated cost of control was $1.70 an acre; (5) to hold down losses the operations would have to be accomplished between May 20 and June 30, 1947 May 20 because it was about the date of general hatching of the tussock moth caterpillars from the egg masses, and June 30 because after that date defoliation of trees would occur to a degree that would perforce kill much of the timber stand.

The report contained many other details, including a description of the fir tussock moth; estimates of flying altitudes above timber for different types of planes; need for aerial photographic maps; estimated days of flying weather and hours of flying weather per day between May 20 and June 30; and the need for supplementary airstrips.

The meeting heartily approved the recommendations for action. This was the first of a series of steps that presented an inspiring example of varied interests that were quickly knit together and acted on decisively, forcibly, and in complete unity for the accomplishment of an objective.

The report was presented to Department of Agriculture officials in Washington on December 6 and to other groups in December and January. It was presented to the Idaho State Cooperative Board of Forestry, which recommended that the State cooperate with the private timberland owners and the Federal Government in control of the infestation. Idaho Senate Bill No. 118, enacted on February 18, cleared the way for cooperative action by the State and Federal Governments. The Idaho State Legislature on March 4 appropriated $210,000 for cooperative forest-insect and pest control. The directors of the Potlatch Timber Protective Association decided unanimously that the Association should carry its share of the costs. Congress appropriated $395,000 for the work.

The essential preparatory measures were many and varied. The nature of the task required administration by one agency; the major timberland owners agreed that the Department of Agriculture should be the one. Accordingly, the Forest Service and the Bureau of Entomology and Plant Quarantine proceeded within their means and existing authorities. The Forest Service delegated responsibility for the administration of the project to the regional forester of the Northern Region at Missoula, Mont. The Bureau of Entomology and Plant Quarantine delegated responsibility for the entomological phases to their regional forest entomologist at Coeur d'Alene, Idaho.

The regional forester designated a project leader for the Forest Service. All preparatory action was carried on by the project leader and one assistant and the leader for the Bureau of Entomology and Plant Quarantine, with the help of the regular divisions of the Forest Service and those of the Bureau of Entomology and Plant Quarantine.

Most of the area in need of treatment was in Idaho. An area of about 4,000 acres just over the line in southeastern Washington also had to be treated because otherwise the prevailing winds would make it a source of reinfestation in Idaho. An area of about 14,000 acres in the Blue Mountains in Oregon was listed for treatment if funds were sufficient.

Cooperative agreements with all the States concerned were essential to set up authorities and responsibilities for various phases. A formal agreement with the State forester and the Land Board of Idaho was signed on April 17, 1947. The most important items of the agreement were: The regional forester at Missoula was designated as agent of the State of Idaho to conduct all phases of the control operations; the Bureau of Entomology and Plant Quarantine was to be responsible for the entomological phases; the State was made responsible for collections of contributions of funds for control from private landowners; the United States was relieved of any public liabilities arising from application of spray on State and private lands; a general formula was set up for sharing costs among private landowners, the State, and the Federal Government; and the spray formula was established as "not more than 1 pound of technical DDT in solvent and fuel oil to make 1 gallon of spray, to be applied at the rate of 1 gallon per acre."

Less detailed agreements were made with the State foresters of Washington and Oregon.

Aerial maps were essential for use of the pilots, for the delineation of infested areas, and for various other controls. Contact prints scaled to about 3V2 inches to the mile and enlargements to 6 inches to the mile were assembled and prepared for use. Their value was increased by adding section lines.

Surveys to determine suitability and location of temporary airstrips were made, and seven such strips were constructed by the Division of Engineering in the Forest Service. The surveys and construction work were hampered by snow and wet ground. The last of the strips was completed shortly after spraying operations began.

The award on bids for aerial-spraying contracts had to be made far enough in advance of the scheduled date of initial spraying operations to allow the flying contractors time to construct and install the spraying equipment. The preparation of bids was difficult because there were no previous contracts to serve as a guide and no definite specifications for spray apparatus for such a job existed. The invitation to bid stipulated that the spray apparatus must regulate application to 1 gallon to the acre and would be subject to flight tests before the start of control operations. Bids were opened on April 14, but were not finally accepted until immediately after the appropriation of the Federal funds. The contractors, despite the short period available for construction and installation of spray apparatus, were ready to fly on May 20.

Procurements of DDT and the finished insecticide were handled by the Washington offices of the Bureau of Entomology and Plant Quarantine and the Forest Service. The quantities of insecticide (350,000 gallons) and the time limit heavily taxed available supplies of DDT and the capacity of the mixing equipment of the contractors. Arrangements were made with traffic managers of the railroad companies to red-tag manifest the spray tank cars and deliver the spray on a schedule which would minimize loss of the limited flying time.

Truck tractors and tank trailers for delivery of spray from the railhead to the airfields were essential. The only source from which these were obtainable was the Army Air Force, which lent the equipment it had at the Spokane Army Airfield.

Arrangements were made with the Weather Bureau to establish a 24-hour weather service at field headquarters in Moscow. June is a month of uncertain weather conditions in this area.

Weather records over a period of years were analyzed and used as a basis for the over-all plans. Even so, there was uncertainty. Abnormal rains and wind occurrence and velocity would seriously reduce favorable flying time.

A detailed survey of the general area of infestation was necessary in advance of spraying to delineate the areas to be sprayed on aerial maps for use of the pilots, to subdivide the infested areas into spray-application units, and to determine accurately the acreage to be sprayed. Because of snow and impassable roads, this precontrol survey was not completed until June 20.