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. 

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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.

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