Tag Archive: Whiteflies

Silverleaf Whiteflies in Panhandle Cotton

Silverleaf Whiteflies in Panhandle Cotton

Sliverleaf whiteflies (SLWF), also known as sweet potato whiteflies, are a major pest in many cropping systems. The SLWF has a broad feeding range of over 600 host plants, which includes ornamental, vegetable, and field crops. This season, large populations of silverleaf whiteflies have been reported in in cotton in Georgia, Alabama, and now Florida’s Panhandle.

Whitefly adults and eggs (photo credit James Castner)

Females deposit eggs on the underside of leaves. Once an egg hatches, the first instar in the SLWF life cycle is referred to as a “crawler.” As the name implies, during this stage the immature instar will crawl on the leaf underside until selecting a location to feed. Once settled, the remaining stages of its life cycle are immobile until it reaches adulthood. Both the adult and immature SLWF have sucking mouthparts, which they use to feed on plant juices. SLWF excrete honeydew, a waste composed largely of sugars. This honeydew provides a perfect enviroment for sooty mold development on the leaf tissue, which can impact photosynthesis, as well as cause the cotton lint to stick together making it difficult to gin. Feeding damage from SLWF can also result in premature defoliation. SLWF populations will increase and pose a threat to cotton until it is defoliated or the leaves drop from feeding injury.

University of Georgia Extension Entomologist, Dr. Phillip Roberts published the article Georgia Cotton: Whitefly Infestations Across the State – What Can You Do? a few weeks ago.  The article discusses thresholds and other key management factors. A summary for most of his article can be found below. Dr. Ron Smith of Auburn University also published the article Silverleaf Whitefly Control in Cotton that also discusses SLWF management.

Scouting Summary:

When scouting cotton for SLWF, select the fifth mainstem leaf below the terminal to check for infestations. Sample at least 30 random plants in the field, avoid edges by moving at least 25 paces into the field and then keep selected plants about 10 paces apart. Treatment is recommended when 50 percent of sampled leaves have 5 or more immature crawlers. Keep in mind that late planted cotton has a higher risk for SLWF infestations, as well as hairy leaf varieties in comparison to those with a smooth leaf.

Whitefly nymphs and pupae (photo credit Lyle Buss)

Treatment Summary:

Insect Growth Regulators (IGRs) such as Knack and Courier are the main component of SLWF management programs in cotton. Their effects on SLWF populations are generally slow due to the stages they target in the insect life cycle, but these types of products have long residual activity. With large infested areas across the southeast, certain products are becoming harder to obtain due to treatment demand. Other products with whitefly activity include Assail, Sivanto, and Venom which target all stages of the insect’s life cycle. Oberon is another product used, which treats primarily nymphs.

It is important to note the role beneficial insects play in the field. Natural enemies of the SLWF include lacewings, minute pirate bug, and some species of ladybug. These types of insects can be conserved by avoiding use of broad spectrum insecticides such as pyrethroids, unless other pest thresholds are reached. Pyrethroids can be identified by looking at the active ingredient listed on a product label, their common name will end in -thrin or –ate. Examples of these types of products include Bifenthrin, Karate, and Orthene.

For more information consult the following articles, or contact your local Extension Agent.

Georgia Cotton: Whitefly Infestations Across the State – What Can You Do?

Silverleaf Whitefly Control in Cotton

 

PG

Author: Ethan Carter – ethancarter@ufl.edu

Ethan Carter is the Regional Row Crop IPM Agent in Jackson County. He earned his BS in Food and Resource Economics, and his MS in Agronomy, both from the University of Florida.

Ethan Carter

Permanent link to this article: http://franklin.ifas.ufl.edu/newsletters/2017/08/25/silverleaf-whiteflies-in-panhandle-cotton/

Unusual Outbreaks of Sweetpotato Whiteflies in the Panhandle

Unusual Outbreaks of Sweetpotato Whiteflies in the Panhandle

Figure 1. Whitefly adults and eggs (photo credit James Castner)

Figure 1. Whitefly adults and eggs (photo credit James Castner)

Xavier Martini, Mathews Paret, Josh Freeman, UF/IFAS North Florida Research and Education Center

Outbreaks of sweetpotato whiteflies (also called silverleaf whitefly) Bemisia tabaci (Figure 1 above) have been recorded recently in the Florida Panhandle and South Georgia on tomatoes and other vegetables. Whitefly is a generalist herbivore insect that feeds on 600 host plants. Sweetpotato whitefly damages plants directly by feeding and cause silverleaf disorder in cucurbits (Figure 2), and irregular ripening in tomato. It also vectors over 111 different plant viruses such as the Squash Vein Yellowing Virus that can kill watermelon plants and results in necrotic areas on the fruit, the Cucurbit Leaf Crumple Virus that is mainly destructive for squash, but also affects other cucurbits, and the Tomato Yellow Leaf Curl Virus that affects tomatoes.

Figure 2. Silverleaf disorder on squash

Figure 2. Silverleaf disorder on squash

This arrival of whitefly is quite unusual at this time of the year in the Florida Panhandle.  Whitefly densities usually increase in October when cotton is defoliated and soybean senesces. This early arrival of whiteflies requires attention given the recent outbreak of Q biotype whiteflies in the Florida landscape. Sweetpotato whitefly is a complex of 28 cryptic species. In the US, the most common are the B and the Q biotypes. The Q biotype is a particular source of concern, as it is more resistant to insecticides than B biotype, and is replacing B biotype in other parts of the world. Since July 2016, Q biotype has been found in 8 counties in Florida, but not in the Panhandle to this point.

Biotype Q and B are indistinguishable visually, and must be discriminated by genetic analysis. The whiteflies collected so far by the NFREC in Gadsden County were all B biotypes, but it is important to pursue the monitoring of our whitefly population to be sure that the Q biotype does not settle in our area.

To sample for biotyping, sample one whitefly per plant, and collect between 10 to 50 whiteflies. Keep whiteflies collected on different host plants separate. Adults can be collected by hand or nymphs, and pupae (Figure 3) can be detached from leaves with a small knife. Store in 95% ethanol or freeze and immediately bring them to the NFREC, or to your local extension agent who can send them to a lab for biotyping. Alternatively, infested foliage can be brought directly to NFREC for processing.

Figure 3. Whitefly nymphs and pupae (photo credit Lyle Buss)

Figure 3. Whitefly nymphs and pupae (photo credit Lyle Buss)

Simple cultural practices can help reduce whitefly damage. Sanitation is one of them. After harvest, crop residue such as tomato plants should be removed to reduce virus reservoirs in the crop. Natural enemies are an important part of whitefly control. It has been found that whitefly outbreaks occurred more often when natural enemy populations are absent, because of repeated insecticidal sprays. Natural enemies of sweetpotato whitefly include parasitoids, lacewing, minute pirate bug and some minute species of ladybird beetles. It is always important to assess the presence of natural enemies before applying an insecticidal treatment.

If whiteflies are present in high density, and natural enemies are not found, insecticide application is advised. Based on experience, these populations will likely need to be managed until early November. It has to be noted, that sweetpotato whitefly is particularly challenging to control with insecticides because they live on the underside of the leaf, and easily develop resistance against insecticides. To optimize insecticidal efficiency against sweetpotato whitefly it is preferable to use systemic insecticides such as neonicotinoid (imidacloprid, thiamethoxam, dinotefuran) and diamides (cyazypyr). Additionally, Pymetrozine (Fulfill) has been found to reduce virus transmission in tomatoes. Foliar application of neonicotinoid should be restricted to the period before flowering because of toxicity to bees. For organic producers, neem oil or insecticidal soap are potential alternatives to synthetic insecticides. Because whitefly is prone to development of resistance, it is crucial to rotate insecticide modes action (which can be found in the Vegetable Production Handbook and on pesticide labels).

For more information, use the following publication links:

Sweetpotato Whitefly B Biotype, Bemisia tabaci (Gennadius) (Insecta: Hemiptera: Aleyrodidae)

Recommendations for Management of Whiteflies, Whitefly-Transmitted Viruses, and Insecticide Resistance for Production of Cucurbit Crops in Florida

Management of Tomato Yellow Leaf Curl Virus (TYLCV) in Tomato in North Florida

Vegetable Production Handbook of Florida 2016-17 (371 pages)

 

 

 

PG

Author: Josh Freeman – joshuafr@ufl.edu

Dr. Freeman’s program focuses on vegetable and melon cropping systems important to the state and region. Much of his research and extension efforts are focused in the area of soil fumigants and fumigant alternatives for soil-borne pest and weed management. Many of the vegetable crops in Florida are produced using the plasticulture production system. For decades growers have relied on the soil fumigant methyl bromide for pest management. This chemistry is no longer available and Dr. Freeman’s program is addressing this issue.
https://www.facebook.com/NFRECVegetable

Josh Freeman

Permanent link to this article: http://franklin.ifas.ufl.edu/newsletters/2016/09/17/unusual-outbreaks-of-sweetpotato-whiteflies-in-the-panhandle/