   Pests of Agaves and Yuccas - July 23, 2008 Jeff Schalau, Associate Agent, Agriculture & Natural Resources University of Arizona Cooperative Extension, Yavapai County Agaves and yuccas are beautiful ornamental plants that are often used to accent xeriscape gardens. For the most part, they do not have serious pest problems. However, there are a few exceptions and learning to recognize their presence is important to maintaining these plants’ health. Snout weevils are probably the most damaging pests to agaves and yuccas. The agave snout weevil (Scyphophorus acupunctatus), also known as the sisal weevil, feeds on many species of agave and can be especially damaging to the larger species such as century plant (Agave americana) and blue agave (Agave tequilana). It will also feed on other agave species. The agave snout weevil is also a serious pest where blue agave is grown commercially for tequila and in foreign countries where agaves have been introduced as landscape plants. A similar species also colonizes yuccas. Snout weevils are beetles about ½ inch (12 mm) in length, brownish-black and have a dull body. Being a weevil, it has a protruding snout and chewing mouthparts. The adult female enters the base of the plant to lay eggs in the spring. These eggs hatch into larvae (grubs) that feed on the succulent core of the plant. Decay microbes also enter through this injury rotting plant tissue causing the plant to collapse. Infested plants soon collapse and die. The larvae have chewing mouthparts and develop in the dying plant and infect other hosts nearby. Control of the agave snout weevil is difficult. Selecting species that are less susceptible and typically smaller than the century plant is helpful, especially in areas where the problem has occurred previously. Minor infestations can be controlled by removing and discarding the affected plants. With rare or special specimens, chemical prevention using a broad-spectrum insecticide applied in spring is often effective in reducing damage. Diazinon granules were once used to control agave snout weevils, but diazinon is no longer available. Imidacloprid granules (Merit) applied in the early spring are a suitable replacement when pesticides are deemed necessary. Leaf-footed plant bugs can also negatively affect agaves and other rosette succulents. Plant bugs have piercing/sucking mouthparts that cause alight yellow-tan scar at the point of feeding. Plant bugs may be controlled by using insecticidal soap or a broad spectrum ornamental plant insecticide. Chemicals should be applied in early morning or late evening when the bugs are most active. Several applications of the insecticide may be needed for complete control. In my landscape, woodrats (packrats) were feeding on my yucca and beargrass plants all winter. I don’t know why they were so bad this year, but maybe it was partially due to lack of other foods. Woodrat damage to agave and yucca is distinguished by removal of leaves using their sharp incisors. They also feed on prickly pear pads and fed so heavily on my peach tree that I hardly had to prune it. I also had a gopher burrowing near some of my agaves and initially, I thought nothing of it. That is, until the center of one and then another collapsed. The gopher had eaten the center out of my two largest agaves from below. I had not observed this ever before, but I imagine it is a common occurrence. The cores of agaves are sweet and this must be a treat for gophers. Similarly, while out surveying some rangelands this spring, some deer flushed out of an area nearby. We noticed they had been feeding on immature agave flower stalks. The agave flowers were at the stage where they looked like giant asparagus spears. Surveying the situation, a colleague took out his pocket knife and cut into the succulent stalk. We tasted it and sure enough, it was sweet and refreshing similar to jicama in flavor. Wild animals and insects know a good meal when they find it. The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at cottonwoodmg@yahoo.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/. |