Rose Pests In Detail

Rose cane nesting wasps

Gardeners become concerned when they notice tunnels in their rose canes or small, sparse, yellow or wilted rose leaves. These conditions are caused by insects which aren't always a detriment to the garden. The most common tunnelers are hunting wasps that, for the most part, are beneficial predators. These small, harmless wasps nest in the rose piths but do not injure the plants. These hunting wasps feed on aphids and provide some degree of insect control.

Female wasps lay eggs on cut canes. The eggs hatch into caterpillars which tunnel into the cane pith. They feed for about two weeks on aphids brought to the nest by the female wasp. After two weeks, the larva goes into a dormant state before emerging as an adult wasp.

If the wasps do significant damage to a plant, prune the rose cane below the wasp nest area where there may be a slight swelling. Seal this cut and routine pruning cuts with water-insoluble glue or nail polish to prevent more nests of eggs. Controlling aphids may also encourage wasps to search for other nesting sites that have a reliable food source.

Rose cane borer

Rose Chafers

There are two species of rose chafers in the genus Macrodactylus in North America. The most common in eastern United States is the rose chafer, Macrodactylus subspinosus (Fabricius) and is found from eastern Canada south to Colorado. The second species is the western rose chafer, Macrodactylus uniformis Horn and it occurs in Arizona, New Mexico, Texas and south into central Mexico. Both species are very similar in size, body shape, and habits. Control measures for one species should also apply to the other.

The rose chafer, Macrodactylus subspinosus (Fabricius), is a tan, long-legged slender beetle from 8-12 mm long. The rose chafers damage plants by feeding on the flowers, newly set fruit and foliage. On roses it skeletonizes the leaves in the same way as other scarab beetles like the Japanese beetle, Chinese rose beetle, and the serica garden beetle. It feeds on on the foliage of many different plants and it is greatly attracted by flowers. The rose chafer is native to the northeast from eastern Canada south to Colorado.I have seen samples from Fenton, MI and Galesville, WI.

LIFE CYCLE: Adult beetles emerge from the soil in late May through early June and and they live for about one month. Mating occurs soon after emergence and the females lays her 24-36 eggs continuoulsy for about two weeks in the soil in grassy sandy areas. Upon hatching the larvae burrow in the soil and feed on the roots of grasses and weeds. The overwinter as a larvae and continues development in the spring. The full grown larva or grub is white and measures up to 18 mm in length. Pupation occurs in the spring. The rose chafer has only one generation per year.

CONTROL: Scouting or monitoring for the presence of rose chafers is very important for adequate control. Rose chafers are most prevalent in areas with sandy soil. Adults readily attracted to many types of flowers and feed on the foliage many plants. The larvae or white grubs feed on the roots of grasses and many cultivated and wild plants. From late May through July, the foliage should be inspected for skeletonized leaves and the presence of adult beetles on the leaves and flowers. Rose Pest Rx and Garden Pest Rx beneficial nematodes are an ideal way to control this pest.

Rose chafers can be handpicked and destroyed if the infestations are light. Rose chafers can be very numerous especially in areas with sandy soils. In these cases insecticides may not give satisfactory control as rose chafers can move in from surrounding untreated areas or the insecticides do not seem to prevent feeding activity for very long. However, after about 2-3 weeks of heavy damage the beetle numbers appear to subside. Insecticides used in the control of rose chafers include carbaryl (Sevin), 

It was interesting to read that birds sometimes die from eating adult rose chafers. The beetles apparently have a chemical that affects the heart of small, warm-blooded animals.

The western rose chafer, Macrodactylus uniformis Horn occurs primarily in Arizona and New Mexico south into Mexico. It resembles the rose chafer and its damage is similar. It is 10mm long and the body is rather slender, long-legged, and yellowish brown in color. Its pubescence is longer and denser than that of the rose chafer. I have collected numerous beetles in southern Arizona and central Mexico feeding on many kinds of plants.

Rose Midges

The rose midge are mosquito-like in shape and they are 1-2 mm in length. They emerge from pupae in the soil early in the spring in synchrony with the production of new plant growth and flower buds. There are several overlapping generations per year and a single generation, or life cycle, can be as short as two weeks. Populations of the midge build up until early fall and the last generation over winter in the ground in cocoons and adult midges emerge the following spring. Females lay their eggs inside the sepals of flower buds or leafy tips. The larvae then hatch from the eggs and damage the buds and rose tips. The full-grown larvae may measure up to 1.8 mm long and are sometimes reddish in color. Pupation usually occurs in the soil but pupae have been observed in the damaged rose tips. They leave the damage tips after which the buds wither, blacken, and die

Rose midge appears to be a native insect to North America. It was first detected in 1886 in New Jersey by a greenhouse rose grower and since it has been recognized from many of the eastern and Midwestern states as well as in Oregon, Washington and Canada. It's appearance in Oregon happened in the last 15 years. The present extent of the infestation in northern California is unknown. It is likely that the rose midge came into California from Oregon on its own. However, the infestation could have also been introduced into California via infested soil or plant materials either sent through the mail or carried from an infested area in North America.

Hoplia beetles

Hoplia beetles are close relatives of the dreaded Japanese and Chinese Beetles. They are day flyers and prefer the flowers of white to whitish flowers. The adults are small about 1/4 inch to 3/8 inch long and somewhat rectangular and dorsally flattened in shape. Their ventral surface are covered with silvery and coppery colored scales while the elytra and dorsal surface is brownish to reddish brown in color. Silvery scales are also found on the dorsal surface giving the dorsal surface a mottle appearance on various shades of brown. There is only one generation per year with the adults emerging from mid March through May in areas from Palm Springs and Cathedral City in southern California to Redding in northern California.

There are several species of Hoplia beetles throughout the United States. The western species, Hoplia callipyge LeConte, is also known as the grapevine hoplia and it appears to be the only species of this group that attacks roses. According to Essig (1926:445) this beetle also feeds on the young leaves, flowers, and fruit of grapes, peaches, and almonds and on the flowers of ceanothus, greasewood, calla lilly, California poppy, magnolia, lupine, olive, orange, and willow, and on the leaves of beans, horse beans, peas, and vetches. On roses the beetles feed on the petals of opening white and light colored roses by chewing small holes and leaving the petals with a lacey appearance. In my garden, they prefer the white flowers of Sally Holmes, Popcorn, Irresistible, Grace Seward, Class Act, and the Apricot Nectar, a peach colored rose.

LIFE CYCLE: Adult beetles emerge from the soil in as early as mid March in southern California and they can be common from late April through mid May in norhtern California. They are present for only about a month in any one area of California depending on the weather. Mating orgies take place on host flowers. The gravid females oviposit in the soil near host plants and upon hatching the larvae burrow in the soil and feed on the host plant roots. They overwinter as a larvae and continues development in the spring. The full grown larva or grub is white. Pupation occurs in the spring. The hoplia beetle has only one generation per year.

CONTROL: Scouting or monitoring for the presence of hoplia beetles is very important for adequate control. Adults are readily attracted to many light colored roses and other flowers. Light colored roses should be inspected from mid March through May for skeletonized petalsthrough July, the foliage should be inspected for skeletonized rose petals and for the presence of adult beetles tucked inside the flowers between the rose petals.

Hoplia beetles can be handpicked and destroyed if the infestations are light. They can also be handpicked and drowned by dropping them into a bottle filled with soapy water. Satisfactory control can be achieved with the application of insecticides such as carbaryl (Sevin), acephate (Orthene), diazinon, and chlorpyrifos (Dursban), Merit, etc. Please read the insecticide label throroughly and as some insecticides such as diazinon can cause phytotoxic reactions to new foliage if applied when the weather temperatures are above 80 degrees F.

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