Plant Diagnostic Lab — Page 5 — Plant & Pest Advisory

May 1, 2023 Steven K. Rettke

Landscape Pest Notes for Early May 2023

Fungal Leaf Spots: Commonly found on the foliage of many plants, fungal leaf spots are largely cosmetic diseases. Most do not interfere with the normal growth & development of the plant. Therefore, within the landscape, fungicides are not normally recommended. Years that have relatively dry spring weather will experience fewer leaf spot infections.

Many fungal leaf spot infections will demonstrate typical symptoms. Surrounding the initial infected spot will be alternating light-dark-colored concentric rings. The darker areas contain plant-defensive chemicals that the plant uses in an attempt to compartmentalize the invading fungus. If the fungus is virulent enough it may have the ability to move past the barrier & infect the tissue outside of it. The plant will respond again & form a new barrier surrounding the infected area. Sometimes these light-dark discolorations can continue until a target appearance forms. Many times, black fruiting bodies can be seen within the center of the light-colored bull’s eye site where the infection originated.

A dark colored halo will often surround the central fungus infection site. The black fruiting bodies can be observed within the central tan area. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)

Alternating light-dark colored concentric rings. The dark rings are composed of plant defensive chemicals the plant uses in the attempt to wall-off the invading fungus. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)

The Landscape Pest Notes Blog for Early May 2023 is listed below & is composed of some commonly observed insect/mite & disease pests occurring within landscape & nursery plants. The insect/mite pests included are andromeda lace bug, lilac borer, boxwood leafminer, spruce spider mite, & horned/gouty oak galls. The disease pathogen pests included in addition to fungal leaf spots are black knot, sycamore anthracnose, Diplodia tip blight, & apple scab fungus.

April 13, 2023 Steven K. Rettke

Landscape Pest Notes for April 2023

Cool, Moist Springs, Aphids, and Lady Beetles: A cool, moist spring will be good for lady beetles, and other predators feeding on aphids. A single lady beetle larva will eat between 200-300 aphids before becoming an adult. As adults, females eat up to 500 aphids before laying eggs! Before applying any treatment sprays against aphids, monitor for predators and consider if the infested plants are in a key location. If not, then let natural predators provide control.

Species of lady bird beetle larva that specializes feeding on aphids. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)

Management of Aphids Using Soaps?: Although the use of insecticidal soap is stated to be a “biorational” pesticide and is recommended within IPM programs, research has indicated that they typically provide less than satisfactory controls against aphids within the landscape. Insecticidal soap is commercially available under the trade name M-PEDE and although aphids are included on the label, the research indicates only a 5% to 10% reduction of an aphid population with a single application when applied at label rates. The M-PEDE label indicates the less than satisfactory controls it achieves against aphids with a single application. Conversely, it is important to emphasize that insecticidal soap will provide outstanding efficacy against adelgids (i.e., spruce galls & hemlock woolly adelgids) and is highly recommended as a control material against these insects (Precautionary note: As similar to oils, some soap sprays may remove the blue coloration on conifers).

Both horticultural oil & insecticidal soap sprays require good coverage to provide effective controls. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)

This blog includes some of the common insect/mite pests often encountered in NJ landscapes during the month of April. They may require monitoring & intervention to prevent plant damage. Also some abiotic concerns & scouting tips are included. The insect/mite pests reviewed are native holly leaf miner, spongy moth, honey locust spider mite, honey locust plant bug, eastern tent caterpillar, southern red spider mite, hemlock woolly adelgid, & hemlock rust mite.

March 23, 2023 Steven K. Rettke

Some Early Spring Insect Pests of Christmas Trees

The accumulation of heat units (Growing Degree Days (GDD) will soon begin to increase rapidly in New Jersey as we approach the early weeks of April. If past histories or present-day monitoring indicate the need for interventions, then the best control windows for numerous insect/mite pests are beginning to occur. The following is an incomplete listing of a handful of some of our early-season Christmas tree insect pests that may need to be scouted & possibly controlled. Those included in this blog are the European pine sawfly, Eastern spruce gall adelgid, Cooley spruce gall adelgid, Nantucket pine tip moth, Pales weevil, White pine aphid, & Pine bark adelgid.

After many years, these slow growing Colorado blue spruce trees are close to reaching their peak selling growth stage as Christmas trees. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)

March 13, 2023 Steven K. Rettke

White Pine Weevil: Overwintering Adults Become Active in March & April

Many arborists & landscapers often find it difficult to prevent white pine weevil pests (Pissodes strobi), because they are typically applying fertilizer & dormant oil treatments during the control window. In the state of NJ, the control window against feeding white pine weevil adults occurs in March & April. Adults over-winter in the duff beneath trees. The WPW adults will often crawl or sometimes fly to the top terminal leaders of pine, spruce, or Douglas-fir trees. Eastern white pine & Norway spruce species are the most severely attacked & the death of the terminal leaders of these trees will often occur.

Treatment timing is critical with this pest and controlling the adult female before egg laying is necessary. Apply preventative sprays (e.g., pyrethroids) only to the terminal leaders during this time. Before mating & egg laying, adults will feed by chewing holes within the central leader & cause a characteristic pitch flow that becomes white in color when dry. Then females will lay eggs in new cut-out holes within the top 12 inches of the leader just below the terminal bud. This blog will describe with the help of photographs the 7-stage lifecycle of this native weevil borer. Control & management options will also be provided.

White pine weevil adults are about 1/4+ inch long & have a long snout with two white spots on back of wing covers. Adults feed at terminal leaders during March & April. Most eggs will then be laid during April & May. (Photo Credit: Michigan State University)

Severe white pine weevil infestations to terminal leaders can destroy two or more years worth of growth to pine, spruce, & Douglas-fir trees. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)

January 26, 2023 Steven K. Rettke

Nostoc in Nurseries: Herbicides to Control the Slippery Slime Threat

Nostoc is a cyanobacterium and is one of the oldest organisms on earth (over 3.5 billion years). It is a primitive growth, like algae, moss, and liverwort. Many years ago, it was incorrectly identified as blue-green algae. Nostoc has no roots, no vascular tissues & is not a plant but it is photosynthetic. It can be found growing within gravel, stones, limestone chips, granite, saturated soils & on-ground cloth within container nurseries. It can tolerate long periods of desiccation but requires plentiful amounts of water for establishment. This cyanobacterium growth can become common & persistent at certain nursery/greenhouse sites where long-term overhead irrigation is done.

Nostoc growing in front of container bay opening. The opening allowed the overhead irrigation to saturate the soil/gravel at entrance. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)

Nostoc growing on ground cloth within a nursery container bay. Creates a serious slipping hazard for nursery personnel. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)

Nostoc is not toxic & does not directly compete with nursery/greenhouse crops or landscape plants, but it can harbor fungus gnats & snails. Nostoc first became a growing concern in nurseries approximately 30 years ago. Slipping hazards are the primary threat this organism poses to nursery & greenhouse personnel. It forms gelatinous masses composed of filaments linked together by protective jelly-like coverings. This creates a surface as slick as wet ice. Nostoc can occasionally be found growing within turf or landscape settings but is not common.

This blog will show with photographic images how Nostoc can be identified & will also review available control options.

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Filed Under: Nursery, Plant Diagnostic Lab

October 12, 2022 Steven K. Rettke

Autumn Pest Review: Soft Scales, Leafminers, Aphids, Mites & Adelgids

AUTUMN PEST REVIEW: Although the season is beginning to wind-down, there are still a number of insect & mite pests that require scouting during the fall weeks. The pests discussed in this blog include soft scale nymphs, boxwood leafminers, white pine aphids, spruce spider mites, southern red spider mites, hemlock rust mites, eastern spruce gall adelgids & hemlock woolly adelgids. The use of low %-rates of horticultural oils this fall can be especially valuable against controlling many of these pests.

SOFT SCALE NYMPH MIGRATIONS: Most soft scale species (exceptions include magnolia, tuliptree, and globose) have 1st instar nymphs that spend July and August feeding along veins on the undersides of leaves of their deciduous host (the use of a hand lens may be needed). During the weeks of late summer and early fall, these nymphs migrate off the leaves onto woody stem tissue and molt into the overwintering 2nd instar stage. The size of the nymphs increases 3-times after molting and their presence is usually observable even without magnification (they can be as large as lenticels). Typically, overwintering soft-scale nymphs have a dark coloration, to help absorb sunlight and maintain body warmth.

European elm 1st-instar nymphs settled along the main vein underneath elm leaf. During the early weeks of fall they migrate from leaves onto the bark to overwinter. (Photo Credit: Cornell University)