Cotton Aphid

Aphids are among the most serious and widespread pests in pomegranate orchards, but they may be sufficiently controlled by natural enemies.

Cotton aphid numbers build up rapidly on growing shoots in the spring and again in the late summer or fall. During the fall months, cotton aphids move into pomegranate orchards from weeds, cotton, melons, and citrus, depositing eggs on pomegranate stems. These eggs overwinter on pomegranate and in the early spring (end of March) the eggs hatch and nymphs move to the leaves and stems on the shoot tips. The first generation that develops from the eggs produces the apterous (wingless) form and the second generation produces both winged and wingless forms. Subsequent generations do not produce eggs, but instead reproduce viviparously (females give birth to nymphs). In the early spring, winged adults fly to other crops such as cotton, melons, and citrus. Cotton aphid can be found year-round on pomegranate leaves and blossoms; however, numbers are highest in spring and fall.

Cotton aphid is highly variable in body size and color. Nymphs and adults of wingless cotton aphids vary in color from yellow to green to nearly black. Nymphs that are developing into winged adults look very different from the nymphs developing into wingless adults: they bear small welts or protuberances on the sides of their bodies that will become their wings.

Reduced shoot growth and leaf damage of pomegranate is not typical with cotton aphid, even if spring numbers are high. Dense colonies can occur on young fruit without causing any visible damage. Occasionally, abundant numbers of aphids in the spring can cause leaf buds to drop, stunting very young trees, or fruit to drop, which is later replaced with smaller-sized, less valuable fruit.

Later in the season, as fruit approaches ripening in August, aphid honeydew that collects between touching fruit may result in rotten spots on the skin. In addition, sooty mold grows on the honeydew on the outside of the fruit, which can be difficult to remove. Aphids clustering on mature leaves produce more honeydew and are less controlled by natural enemies than aphids growing on shoots and fruit.

Aphid management tactics vary depending on the severity of the infestation and include biological control and insecticides.

Biological control can be effective in controlling aphids, especially in the spring.

Parasites include:

• Lysiphlebus testaceipes (Aphidiidae)

Predatory lady beetles (Coccinellidae) include:

• Ashy gray lady beetle, Olla v-nigrum
• Nine-spot lady beetle, Coccinella novemnotata
• Multicolored Asian lady beetle, Harmonia axyridis
• Convergent lady beetle, Hippodamia convergens

There are also predatory larvae, such as:

• Syrphid flies (Syrphidae)
• Cecidomyiid flies
• Lacewings

Natural enemy control slows during the heat of summer and early fall, but heat also suppresses the aphids. In the fall, as aphid numbers increase, biological control also increases.

Ants hinder natural enemies, and so reducing ant numbers will improve the success of biological control.

Maximize tree health (proper nutrients and irrigation) to help trees withstand pests. Aphid numbers increase easily on stressed trees.

Pyrethrins (Pyganic), azadirachtin (Aza-Direct), neem oil (Trilogy), and peppermint plus rosemary oil (Ecotrol) are all acceptable for use on organically grown pomegranate. Coverage is very important to achieve efficacy with these products and persistence is very short. Multiple applications may be needed. Treatment of overwintering eggs will result in the best control.

In the winter and early spring, monitor for cotton aphid by searching for black eggs deposited on twigs. In the very early spring, when buds begin to break, the eggs hatch and the nymphs move to the new foliage. From March through June aphids are most numerous on the tips of branches where the new foliage is produced. During the summer, aphids may be difficult to find, but then in late summer their numbers may begin to increase.

In areas with weak trees and where natural enemies are not sufficient to lower high aphid numbers, pesticide application may be needed. Short-term control can be achieved with pyrethrins (Evergreen), azadirachtin (Aza-Direct), neem oil (Trilogy) and rosemary plus peppermint oil (Ecotrol). Two or more applications may be necessary. However, these products are fairly selective, allowing natural enemies to survive and assist with control.

The best time to apply imidacloprid (Admire Pro) or clothianidin (Belay) through the drip system is in October. Imidacloprid and clothianidin cannot be applied from prebloom (bud elongation in February) through bloom (August) due to bee hazard issues or when fruit is on the tree (June–October). Additionally, systemic imidacloprid takes several weeks for uptake, so apply it in October to reduce egg-laying and the number of overwintering aphids that emerge in spring. Clothianidin has a more rapid systemic uptake than imidacloprid.

Be aware that the broad-spectrum foliar imidacloprid (Admire Pro) and methomyl (Lannate) can disrupt biological control of other pests such as mealybugs, caterpillars, and soft scale, causing secondary outbreaks of these pests. Do not apply imidacloprid during bloom (to protect bees) or when fruit is present in the orchard. Methomyl is also toxic to bees; do not apply it when bees are actively foraging.