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March 28, 2007

Christmas Tree Scouting Report #1- March 28, 2007

Weekly newsletter compiled by Sandy Gardosik, PA Department of Agriculture.

Welcome to the 2007-growing season. White pine weevil adults were found in traps in Berks, Chester, Columbia, Lebanon, Northumberland, Perry, Schuylkill and York counties. With the warm temperatures on Tuesday I received calls from growers who are monitoring traps for adult emergence. Pyramidal trunk traps, also know as Tedder traps, is an easy and effective method of catching first emergence white pine weevils. Place traps within the row beside a tree that was damaged the previous year. Traps must be baited with gum turpentine and denatured alcohol, which are placed in separate bottles and hung below the funnel trap to be effective. Appling a registered insecticide within a few days once weevils appear in traps followed by a second spray 7 to 10 days later, if damage was heavy the previous year, results in good control. Only the top 1/3 of trees needs to be sprayed since this is where the weevils will feed and mate. Once weevils begin to emerge females begin to lay eggs within two week. Eggs are laid under the bark below the top cluster of buds on the main terminal. Once eggs are under the bark, chemical controls are no longer effective. More information on purchasing traps and making your own can be found on our web site. In 2006 a new class of chemistry was tested for the white pine weevil in Schuylkill County. Avaunt manufactured by DuPont with the active ingredient indoxacarb was approved for apples and pears in 2001. Avaunt controls a broad-spectrum of pests including the Plum curculio weevil and showed good results on the white pine weevil. PDA approved a "special local needs" for DuPont to allow Avaunt insecticide to be used on ornamental conifers to control the white pine weevil (Avaunt label).  Avaunt is a reduced risk pesticide with very low mammalian toxicity and a benign profile for avian and aquatic toxicity. Dried residues of indoxacarb do not significantly affect beneficial insects.

Another early spring pest to be scouting for now is the Eriophyid mite. Eggs are just beginning to hatch in Dauphin County.  This mite is also known as a rust mite because of the damage it produces when populations get high. It's usually the damage produced by these mites that alert growers to the presence of this cool season mite. Damage is usually seen on Norway spruce and Colorado blue spruce. In early spring look for bronzing to the needles on Norway and a silvering to the needles on blues. Eggs are half the size of spruce spider mite eggs, cream in color and can be found on the bottom surface of needles near the base . Adults are light pink, wedge shaped, and have only two pairs of legs. The eggs and adult mites are not visible to the naked eye so a 10-20x-hand lens is needed to see if mites are present. Eriophyid mites are not susceptible to control with the standard miticides. Check the insecticides and miticides sheet for the state of PA.

If you did not have the time to spray for Cooley spruce gall adelgids on Douglas fir and Colorado blue spruce and the Eastern spruce gall adelgids on Norway spruce last fall, now is the time. The overwintering nymphs are exposed and vulnerable to chemical controls at this time. As the warm weather progresses developing nymphs will begin to produce white cottony wax over their bodies preventing chemical control.  Look for the nymphs of the Cooley spruce gall adelgids on Colorado blues and the eastern spruce gall adelgids on Norway's clustered around the base of this year's buds. Cooley spruce gall adelgids on Douglas fir can be found on the bottom of needles.

A number of growers in Pennsylvania have commented that Swiss Needlecast (SNC) on Douglas fir is especially severe this year.  Although no surveys have ever been conducted to support or refute this statement, observations by some growers and specialists concur that SNC in PA has increased in severity, incidence, and distribution over the past several years.

Growers should be familiar with Rhabdocline, the other needlecast disease that affects Douglas fir.  Rhabdocline and SNC can, and frequently do, occur in the same plantation, on the same tree, and even on the same needle.  Determining which needlecast is present, or if both are present, is key to controlling these diseases. The fruiting bodies of SNC are easily detected and can be seen with a hand lens anytime throughout the year. Look for two bands of tiny black structures arising from the stomata on the undersides of the needles. These structures may occur on all ages of needles, even on needles that appear healthy, so it is important to examine many needles on a tree, not just current year symptomatic needles.  Fruiting structures found on older needles that are attached to the tree are still capable of releasing spores.

Fungicides used to control needlecasts are protectants, and in order to be effective they need to be in place to protect the newly expanding foliage during the active period of spore release.  It is not difficult to determine when Rhabdocline fruiting structures are mature and when spores are being released.  During budbreak the structure will swell and the epidermis of the needle will split, exposing an orange mass of spores.  The timing of spore release for SNC is not as easy to determine because there is no obvious visible change to the fruiting bodies.  The most current spray recommendations for the control of SNC are based on those given for Rhabdocline.  Sprays for SNC should begin between the second and third sprays for Rhabdocline or when new shoots are 1 ½ inches long.  It is recommended that an additional fourth spray (applied three weeks after the third spray) be added to this program if SNC is present.  Effectiveness of this program for control of Rhabdocline can be determined the following winter by scouting for symptomatic current year needles.  However, determining efficacy for SNC is not as easy since infected needles may remain attached, appear healthy, and serve as a source of spores for subsequent years.  It should be assumed that fruiting structures on any needle of a tree might indicate a potential disease situation.