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Extension Entomology

Tag: honeydew

Alfalfa Update

–by Dr. Jeff Whitworth, Dr. Holly Schwarting & JR Ewing

Alfalfa weevil larvae have been hatching throughout north central and south central Kansas for the last couple of weeks.  However, as of 9 March, there doesn’t seem to be much feeding or development yet (Photo1).  There are also a few of these tiny larvae that are dead (Photo2).  Because these larvae are so small and vulnerable it is difficult to determine the cause of death.  At least some of the mortality could be related to weather fluctuations that have reached mid 70’s for several days but also dropping into the mid to low 20’s some nights.

 

 

 

Most of these larvae are so small that they are well enclosed within the plant terminals to the point that they cannot be dislodged by shaking the stems into a bucket, as the most accurate sampling method specifies.  This can definitely cause you to underestimate larval populations.  Probably the easiest solution is to hold off sampling until the middle of next week, if the weather turns cooler as predicted.  There are a few more mature larvae present, along with adult weevils (Photos 3, 4). Adults will probably continue depositing eggs for a few more weeks, thus extending the period of larval hatching.

 

 

There are also a few pea aphids present.  Populations do not seem to be increasing now, and there are lady beetles and parasitoid wasps actively attacking these aphids.  Also, reports of cowpea aphids in south central Kansas bear watching.  These aphids are usually more numerous in warmer summer months.  They can add stress to plants by feeding, but they also produce copious quantities of honeydew which can become covered with sooty mold.  This may further stress alfalfa by interfering with photosynthesis, especially with small plants coming out of winter dormancy and experiencing dry conditions and fluctuating temperatures.

 

 

 

 

Sugarcane aphids still hanging on!

–The KSRE Field Crop Entomologists Team

Sugarcane aphid populations continue to persist in sorghum across much of Kansas, but cooler temperatures are slowing them down considerably. However, monitoring populations is still strongly encouraged as infestations can grow quickly if temperatures warm up. Winged aphids are moving from early planted sorghum fields to late planted fields, so pay close attention to whether infestations are winged or wingless. Wingless aphids have the potential to increase rapidly, but several factors, including presence of natural enemies, can help slow population growth. In all cases, be sure to monitor populations closely. Bottom line: scout often.

photo-sep-20-12-28-09-pm
Winged aphids (alates).

Yield loss due to aphid feeding can occur up through black layer. However, most losses caused by sugarcane aphid occur between boot stage and up through soft-dough (50% dry weight in the seed) stage; more data is needed to understand losses between hard dough and black layer, but seed weight (grain quality) and total yield may be reduced. Further details about sorghum growth and development can be found here (MF3234.pdf).

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Lady beetle eggs in a sorghum head.

Harvest of early-planted sorghum is underway, and late-planted fields are only a couple of more weeks from being ready (depending on weather conditions). Most decisions to spray for sugarcane aphid this time of year are aimed at avoiding mechanical issues associated with high aphid numbers and honeydew coating leaves and heads. Although buildup of honeydew can cause significant harvest problems, this is not an inevitable outcome. Weathering can reduce honeydew stickiness, so once grain is fully ripe, delaying harvest for a week or two may be an option, provided there is no indication of lodging. As lower leaves senesce or die off, aphids migrate to the upper leaves and eventually into the heads. We have observed this behavior in several fields this fall. However, colder overnight temperatures will significantly retard aphid growth and reproduction, and significant aphid mortality may occur before freezing.

Aside from honeydew and potential mechanical issues, lodging can also be associated with high aphid populations. It is important to understand that sugarcane aphid is not the only pest in sorghum this fall. We have observed high levels of 2nd generation chinch bugs feeding behind panicle leaf sheaths, which can also weaken stalks and cause lodging. In addition, from a plant physiology standpoint, during the last weeks of grain filling sorghum stems tend to shrink due to natural plant remobilization process, affecting final stalk strength.

When making a decision to treat so close to harvest, growers should consider four main factors: 1) overnight temperatures, 2) stage of crop maturity and potential yield, 3) aphid density, and 4) and the preharvest interval for registered insecticides. If the aphids have been heavy, but your grain has turned color, you may want to wait until the honeydew weathers to become less sticky before trying to harvest it. Read and follow the insecticide labels. For Sivanto and Transform, the preharvest interval is 2 weeks. Follow forecasted temperatures for upcoming weeks. Cooler nights will slow populations. We’ve observed aphids killed by 10 hours at 46F in a small lab study, but more data are needed to understand what low temperatures, for what period, will kill them under field conditions.

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Sugarcane aphids after exposure to freezing temperatures.

Again, monitoring fields and relying on more than a single sampling event will provide additional information for making a treatment decision. The only reason to treat aphids past black layer is to avoid potential harvest issues. Killing aphids this fall will not impact aphid populations next year in Kansas. This is a migratory pest and will not overwinter in Kansas.

Sorghum Update

–by Jeff Whitworth and Holly Schwarting

Double cropped sorghum in north central KS seems to have a significant infestation of “ragworms”.  The larvae are a combination of fall armyworms and corn earworms and are of various sizes.

corn earworm_ragworm

windowpane ragwormfall armyworm_ragworm

 

Leaf feeding in the whorl by either species is highly visible but should not have a significant effect on the plants or yield.

windowpane ragworm

ragworm feeding

Also, most fields in north central KS are infested with aphids.  Corn leaf aphids can produce a great deal of honeydew but mostly in the whorls.  This honeydew may retard head extension but usually does not affect many plants over a large area.

corn leaf aphids

greenbugs

Yellow sugarcane aphids

Also found greenbugs and yellow sugarcane aphids.  None of the invasive sugarcane aphids were detected in north central Kansas.  However, many beneficials are, and will continue to be, present in sorghum fields as evidenced by the numerous green lacewing eggs and lady beetle eggs.

lacewing eggs

European Fruit Lecanium Scale: Adding a “Decorative Touch” to Bald Cypress

–by Dr. Raymond Cloyd

The European fruit lecanium scale (Parthenolecanium cornii) is quite noticeable on bald cypress (Taxodium distichum) twigs and branches. The damage associated with this scale, which depends on the extensiveness of the infestation, includes plant stunting and wilting. The European fruit lecanium scale is a soft scale, so honeydew (a sticky, clear liquid) will be produced during feeding. The honeydew serves as a substrate for black sooty mold and attracts ants. In addition, honeydew can drip onto vehicles parked underneath infested trees leaving unsightly residue.

The scales are dark brown, 1/8 to 1/4 inches in diameter (Figures 1 and 2). Some scales may have white markings on the body. European fruit lecanium scale overwinters as an immature on twigs and branches with maturing occurring in spring. In May and June, females lay many eggs underneath their bodies. In June eggs hatch into small tan-colored crawlers. The duration of an egg hatch can last several days depending on the temperature. Crawlers migrate to leaf undersides and subsequently feed on plant fluids until late summer. At that point, the crawlers migrate back onto twigs and branches to complete their development the following spring. There is one generation per year in Kansas.

Figure 2. MatureEuropeanFruitLecaniumScaleonBaldCypressMay2016 Figure 1. MatureEuropeanFruitLecaniumScalesonBaldCypressMay2016
Figure 1 & 2: Mature European Fruit Lecanium Scale on Bald Cypress

Management of European fruit lecanium scale primarily involves timely applications of insecticides. Applications should be made when crawlers are present because the crawlers are most vulnerable life stage to insecticide sprays. Mature scales possess a shell-like covering that protects them from exposure to insecticides. Repeat applications will be required as the eggs do not all hatch simultaneously but may hatch over a three to four-week period. The most appropriate time to apply insecticides is in late June to early July when the crawlers are feeding on leaves; thus enhancing their exposure to any spray residues. There are a number of insecticides, with contact activity that are effective in suppressing populations of the European fruit lecanium scale. However, many have broad-spectrum activity and will kill many natural enemies including: parasitoids and predators. In fact, most out-breaks of scale insects are caused by the indiscriminate use of pesticides (insecticides and miticides). Therefore, always read the label and exercise caution when applying any pesticide. In the winter, dormant oils can be applied to kill overwintering scales by means of suffocation.

I need to acknowledge Jeff Otto of Wichita, KS for bringing to my attention that European fruit lecanium scale was active. I have also observed infestations in Manhattan, KS.

Spirea Aphid: Watch out for this “Sucking” Insect

–by Dr. Raymond Cloyd

Spirea aphid (Aphis spiraecola) is present feeding on spirea (Spiraea spp.) plants in landscapes. Spirea aphid colonies aggregate on terminal growth (Figures 1 and 2) and their feeding causes leaf curling and stunted plant growth. Spirea aphids prefer to feed on stems and leaf undersides of succulent plant growth. All mature aphids are parthenogenic (reproduce without mating) with females giving birth to live nymphs, which themselves are females. Eggs are laid on bark or on buds in the fall by wingless females after having mated with males. Eggs hatch in spring, and young nymphs develop into stem mothers that are wingless. Spirea aphid females are pear-shaped and bright yellow-green. Stem mothers reach maturity in about 20 days. Each spirea aphid female can produce up to 80 offspring or young females.

Figure 2. SpireaAphidsAggregatingonTerminalGrowthofSpireaPlant
Figure 1: Spirea Aphids Feeding on Spirea Plant

Figure 2. SpireaAphidsAggregatingonTerminalGrowthofSpireaPlant
Figure 2: Spirea Aphids Aggregation on Terminal Growth of Spirea Plant

Although the aphids produce honeydew (sticky, clear liquid); continual rainfall will wash the honeydew off plants. In the summer, both winged and non-winged aphids may be present. The winged forms usually appear when conditions become crowded on infested plants, in which they migrate to a more suitable food source, such as another spirea plant to start another colony. Heavy rainfall and strong winds will dislodge spirea aphid populations from plants onto the ground, where they eventually die. Frequent applications (twice per week) of forceful water sprays will quickly remove spirea aphid populations without disturbing natural enemies such as parasitoids and predators. They have a number of natural enemies including: ladybird beetles, green lacewings, and hover flies that may help to regulate spirea aphid populations.

Spirea aphids are, in general, exposed to regular applications of pesticides such as insecticidal soaps (potassium salts of fatty acids) and/or horticultural oils (petroleum, mineral, or neem-based) that may be effective in suppressing populations of spirea aphid. These pesticides have contact activity only, so thorough coverage of all plant parts is important. Furthermore, these pesticides are generally less harmful to natural enemies compared to conventional pesticides.

Soybean Aphids

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Soybean aphids were detected in north central Kansas on 21 August (see photo).  These aphids have been observed every year since 2002, when they were first detected in Kansas, but have rarely reached populations that stressed plants.  Double cropped fields just reaching reproductive stages could be most susceptible if these populations increase.  Probably the easiest way to find soybean aphid colonies that are just starting is to look for ants on soybean plants (see photo).  If you sweep net soybean canopies and find ants in your sweep net, this indicates there are aphids in the field.  Ants are phenomenal at finding these aphids when they are just beginning to produce honeydew.  Or, if you are scouting plants and see ants on the plants, again, that indicates that soybean aphids are nearby producing the honeydew that ants are interested in. For more information on the soybean aphid, please visit: http://entomology.k-state.edu/extension/insect-information/crop-pests/soybeans/sba/

soybean aphids group

 

soybean aphid and ants

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