| | | --- | | Rhubarb Compendium Quick Index Home Rhubarb Background Rhubarb Festivals Rhubarb History Growing Rhubarb Rhubarb Items Culinary uses Rhubarb Recipes Medicinal Uses Other Uses Rhubarb Toxicity Disclaimer Contact Sub topics of Growing Rhubarb Rhubarb Weeds Rhubarb Bacteria Rhubarb Insects Rhubarb Pests Forcing Rhubarb Rhubarb Propagation Rhubarb Varieties Rhubarb Sources | Rhubarb Pests & ProblemsInsects and BugsRhubarb Curculio Description: The rhubarb curculio, Lixus concavus, is a large (about 1/2 inch, 13 mm), dark gray, snout beetle dusted with a yellow powder that easily rubs off when the insect is handled. The head has a long, curved snout at the end of which are the mandibles. It damages rhubarb by puncturing stalks and laying eggs into them. However, the larvae feed and develop on curly dock, which is also sometimes known as wild rhubarb. The eggs are oblong and yellowish-white in color, while the mature larva is a 3/4-inch legless grub with a brown head capsule. Symptoms: Rhubarb curculio injury may be either feeding injury (which appears as notches in the rhubarb stem and on the leaf edges) or egg-laying punctures in the stem. Feeding injury often leads to stem decay as other organisms invade the injured tissue. Sap exudes from wounds of either type and collects as glistening drops of gum when fresh. Fortunately the eggs of this insect do not hatch when deposited in rhubarb. The leaf stalks of the rhubarb may show exuding sap and partial decay from late spring through early summer due to the feeding and egg-laying punctures of the rhubarb curculio. BollWeevil.jpg (10449 bytes) Rhubarb curculio (photo credit) Life Cycle: The curculio over-winters as an adult is piles of debris or in other protected places. The adults appear mid summer and are seen resting on the stalks and leaves of rhubarb, dock, thistle, or sunflower. They soon begin laying eggs. Eggs are deposited singly in cavities about 1/8-inch deep in the stalks. Hatching occurs in 7 to 10 days in all plants except the rhubarb. Eggs deposited in rhubarb are crushed by the actively growing plant tissue. The newly hatched larvae burrow their way down through the weed stalk, reaching maturity in 8 to 9 weeks at the bottom of the stalk just below the soil surface. Usually only one grub reaches maturity in a host plant. Pupation occurs in a cavity at the base of the host plant. Within a few weeks, the adult beetles emerge and feed for a short time before seeking out protected places to pass the winter. There is only one generation a year. The rhubarb curculio completes its life cycle in weeds in or near the garden. It damages rhubarb only through feeding and oviposition. Control: - Handpicking the beetles from the plants during early summer and destroying them is the only direct method of control. When the beetles first emerge, they are easily picked from the vegetation on which they are resting. Their large size aids in finding them and helps make them easy to handle. - The removal of all wild plants in which the beetles breed (curly dock, thistle, and sunflower) growing in or near the rhubarb planting during summer (while the curculio larvae are still in them) will also be helpful. 18,32,85,86,87,88 AphidsI have had a minor problem with aphids (Genus Aphis and Macrosiphini) on a few of my rhubarb plants. Most aphid species are relatively host-plant specific, although they may occasionally be found colonizing certain plants or âreserve hostsâ with which they are normally not associated. The Aphidoidea are predominately a north temperate group (North America, Europe, Central Asia). Almost all major pest aphids are introduced species. Description: Aphids are small, soft-bodies insects about the size of rice grains (typically range in size from 1/16 - 1/8 inch or 1.5 - 3.5 mm in length). They are usually light green or black with a white wooly coating. Aphids survive by sucking the juices of soft new growth which damages a plantâs ability to properly process food, reducing the plants vigor and causing distorted growth in severe cases. Symptoms: Check newly forming leaves and buds for aphids and also look for distorted yellow leaves with a grayish cast. Aphids also leave a sticky coating on leaves from an excretion called âhoneydewâ. insect2_7.jpeg (52958 bytes) Aphid Life cycle: The life cycle of aphids is rather unusual and can be complex. Most aphids reproduce sexually and develop through gradual metamorphosis (over wintering diapause egg, nymphs and winged or wingless adults) but also through a process called âparthenogenesisâ (the production of offspring without mating, asexually). Sexual reproduction involves gene recombination while parthenogenesis does not. The life cycle (development to sexual maturity) for most aphids is 5 to 6 days. Under greenhouse conditions the cotton aphid may complete a maximum of 51 generations a year, with each adult producing about 85 young. Sexual maturity is reached in 4 to 10 days and the reproductive period is about three weeks. The average length of life of an adult is about one month. Parthenogenic green peach aphid females, Myzus persicae, can produce three to six fully formed young per day for several weeks. Host alternation is common in aphids. Often, aphids use one host plant as the âprimary hostâ for reproduction and another plant (perhaps a distantly related plant) as a âsecondary hostâ for parthenogenetic reproduction. 89,90,91,92 | | | | --- | --- | | mini76.gif (138 bytes) A huge document on Aphid Management (or here) | mini76.gif (138 bytes) Organic Pest Control mini76.gif (138 bytes) Organic Gardening From Down Under |