By Douglas G. Pfeiffer, Dept. of Entomology, Virginia Tech, Blacksburg VA 24061
In January 2020, at the Southern Fruit and Vegetable Conference, a group of berry specialists met to discuss current issues in blackberry culture and pest management. This was for the purpose of producing a Pest Management Strategic Plan, an effort led by Gina Fernandez of North Carolina State University. PMSP documents serve as a source of information, ranking problems for an industry to inform decision making, grant writing, and regulatory decisions. Great progress is being made in bring this report to fruition, and while it is not yet published, I’d like to discuss some points regarding entomological aspects. An important component of the PMSP is the ranking of research priorities as well as ranking of pests’ importance – insects, diseases, and weeds. While insects and mites are considered separately in the document, for this discussion I will consider them together as arthropods.
Priority problems: It will come as no surprise the top ranked research priorities is spotted-wing drosophila. This pest has been a game changer since it moved through the Southeast from 2009-2011 (Burrack et al. 2012). In the Summer 2020 issue of Small Fruit News, there were two articles on SWD, covering conventional and organic management of this insect (Pfeiffer 2020, Sial 2020). SWD can be devastating pest of caneberries, and the tolerable levels are so low, there is a heavy reliance on chemical control. This poses several problems: 1) with its high reproductive rate and high number of annual generations, there is a high risk of insecticide resistance, 2) with elevated insecticide use comes an elevated chance of residues at harvest, a problem in both domestic and international markets, and 3) many of the most effective insecticides are highly disruptive to beneficial arthropods (related to this is the long PHI, or preharvest interval with some of these products). This leads to induction of secondary pests, like spider mites. The PMSP document will consider these problems as needs that must be addressed by the industry. There is a need to keep bifenthrin and malathion as pesticide management tools, but there is also a need for less disruptive chemistries. The PHI for bifenthrin, Asana (esfenvalerate), pyrethroids) is too long. More cultural practices/management research is needed. Marketers have zero tolerance for SWD in berries, which makes this a very high priority for research. Complicating the SWD situation, with high rates of chemical control use, secondary pests are emerging.
Two arthropod-related topics fall into Rank 2 in importance: broad mites, and some general pesticide issues. Broad mite is mite that is not as well known as spider mite, and seems to vary in severity across the region. It causes distorted leaf growth, reduced leaf area and water content in its various hosts (Peña and Bullock 1994). It was first reported from blackberry where it caused leaf-curling in 2007-2009 (Vincent et al. 2010). There is a sexual dimorphism in broad mite, and other tarsonemid mites. The female pupa is attractive to males – a male will pick up a pupa, carry it around on his back until the adult female emerges, whereupon mating occurs. Like spider mites, broad mites exhibit haplo-diploidy, meaning that fertilized eggs give rise to females, and unfertilized eggs give rise to males. Normal dispersal is accomplished by males carrying females off, and this may be facilitated by another means. At times, broad mite is phoretic (hitch-hiking) on whiteflies (Palevsky et al. 2001). The PMSP points out the need for more chemical control tools and for more research on cultural practices in management of broad mite. It is known that there are differences in susceptibility among blackberry lines (Vincent et al. 2010). Hot water soaks of potted host plants can be an effective control tool, but this is relatively impractical for caneberry plants in the field!
Pesticides were also discussed as Rank 2 – There are several issues relating to chemical control that were pointed out by respondents. There is a need to keep malathion and bifenthrin as management tools. A pesticide issue included as Rank 3 is the need for better broad-spectrum chemistries during harvest. A common problem is that PHI values are too long to deal with pests that feed on caneberries at harvest time.
Spider mites ranked in the third tier of blackberry concerns. They will be an emerging problem in tunnels; they are often more problematic in greenhouses and tunnels than in field settings. There should be more cultural practices/management research for spider mites.
General aspects of pest management programs are covered by the PMSP. Seasonal ‘at a glance’ calendars are provided for both fungicides and insecticides. The report refers the reader to an existing publication for further information on caneberry pest management. The Southern Region Small Fruit Consortium produces separate guides for each of the small fruit crops grown in the Southeast, and this includes caneberries (Oliver et al. 2020). These are revised annually by small fruit specialists throughout the regions. The collection of guides can be found at the Consortium web site (https://smallfruits.org/ipm-production-guides/).
Arthropod pest rankings: While several arthropod pests were rated in the overall discussion of issues of importance, there is a separate section that ranks the importance of blackberry pests. In this discussion of arthropod pests, I will combine mites along with insects, despite their being treated separately in the PMSP.
High: brown marmorated stink bug, green June beetle, Japanese beetle, raspberry crown borer, red imported fire ant, spotted-wing drosophila, broad mite (in places), twospotted spider mite
The species in this category pose major management concerns for blackberry growers. I mentioned above SWD, and don’t need to elaborate more now, except to say the need continues for sensitive predictive tools, resistance management options, and non-chemical means of control. I also touched on broad mite. The document mentions a caveat on broad mite importance – “in places”. It will be important to follow the course of broad mite, to see if it becomes more of a general issue. The same can be said for imported fire ant. This has been a problem in the Deep South, of little importance in the northern part of our region. However, fire ant is now spreading in Virginia (Miller and Allen 2019), and could come to present problems for blackberry production there as well. Brown marmorated stink bug is a relatively new component of the stink bug community, and is the most problematic of this family. Not only does it feed on buds and berries, but is outcompeting other, less damaging stink bugs in caneberries (Basnet et al. 2014). Twospotted spider mite is the most agriculturally important mite in the world, and is the main spider mite pest on caneberries. Resistance management is especially critical for spider mites because of their propensity for developing resistance, and so alternative control as especially important. While Japanese beetle and green June beetle are mainly foliar feeders on some crops, they cause direct injury to fruit in caneberries. They can invade plantings as berries are ripening, and being harvested. It will be very important to have alternative controls, and chemical control tools that can be used at this sensitive time. Raspberry crown borer is a moth whose larva feeds in the crown of the caneberry plant, around the ground line. This could be a problem especially in a nursery settings. Infestations are more cryptic than other borers, and infested plants could be shipped to commercial operations.
Medium: blackberry gall midge, flower thrips, green stink bug, raspberry cane borer, rednecked cane borer, Euschistus sting bugs
Green stink bug and brown stink bug have long been pests on fruit crops, and fit in the middle category of importance here. They are not as significant a problem as BMSB. Thrips can be an issue with caneberries, especially in some years, and there has long been a problem in having an adequate suite of insecticides to use in accordance with resistant management. Further information is needed on the importance of thrips-borne viruses in caneberries. Raspberry cane borer and rednecked cane borer can be problems as well, and infestation can reduce yields. Their infestations are more obvious than raspberry crown borer, and as less difficult to deal with. Blackberry gall midge is one of several gall midges that can damage blackberry leaves of blossoms. Effective sampling methods and control protocols are needed.
Low: Blackberry psyllid, leafrollers and leaftiers, rose scale, sharpshooter leafhoppers, strawberry bud weevil, redberry mite
Pests in this category can cause localized problems, but have not risen to the level of widespread concern. Blackberry psyllid can cause reduced cane growth in blackberries (not affecting raspberries), especially if near stands of conifers. Leafrollers have not caused significant problems in recent years. Sharpshooters are xylem-feeding leafhoppers, known especially as vectors of Pierce’s disease of grapevines. Strawberry bud weevil is not an important here as it is in strawberry, but can also clip the buds of blackberry.
Emerging: Aphids, mealybugs, sap beetles, whiteflies, yellowjackets
Some emerging pests are growing in severity because of spray programs that eliminate natural enemies. This is especially important with aphids, mealybugs and whiteflies. They will thus be affected by progress made in developing non-disruptive controls for the pests discussed above. Yellowjackets can be problematic because the wasps feeding on berries come and go from their nests, and killing them with insecticides does not address their source.
Chemical controls: The PMSP document will lay out the currently available insecticides/acaricides. As expected in a PMSP such as this, the list of pesticides is a snap shot. Included will be common and trade names, as well as PHI and REI values. A table is included that presents efficacy of the various materials for specific pests. This will be a useful source of information to pest managers in arranging their spray programs, but will serve as a point of discussion on advantages and disadvantages of specific products, and addressing regulatory needs. Much of the information in this section is also available in the pest management guides mentioned earlier.
Basnet, S., L. M. Maxey, C. A. Laub, T. P. Kuhar, and D. G. Pfeiffer. 2014. Stink bugs (Hemiptera: Pentatomidae) in primocane-bearing raspberries in southwestern Virginia. J. Entomol. Sci. 49: 304-312.
Burrack, H. J., J. P. Smith, D. G. Pfeiffer, G. Koeher, and J. Laforest. 2012. Using volunteer-based networks to track Drosophila suzukii (Diptera: Drosophilidae) an invasive pest of fruit crops J. Integ. Pest Manag. 3: B1-B5.
Miller, D., and H. Allen. 2019. Red imported fire ant (RIFA). VCE Publ. 444-284 (ENTO-342NP). 9 p.
Oliver, J., G. Schnabel, R. Melanson, N. Gauthier, M. H. Ferguson, H. Burrack, S. A., F. Hale, D. Pfeiffer, W. Mitchem, K. Jennings, D. Lockwood, M. T. Mengak, G. Fernandez, and E. Stafne. 2020. 2020 Southeast Regional Caneberries Integrated Management Guide.
Palevsky, E., V. Soroker, P. Weintraub, F. Mansour, F. Abo-Moch, and U. Gerson. 2001. How species-specific is the phoretic relationship between the broad mite, Polyphagotarsonemus latus (Acari: Tarsonemidae), and its insect hosts? Exp. Appl. Acarol. 25: 217-224.
Peña, J. E., and R. C. Bullock. 1994. Effects of feeding of broad mite (Acari: Tarsonemidae) on vegetative plant growth. Fla. Entomol. 77: 180-184.
Pfeiffer, D. G. 2020. Conventional management of spotted-wing drosophila, Drosophila suzukii (Matsumura). Small Fruit News 20: https://smallfruits.org/2020/2007/conventional-management-of-spotted-wing-drosophila-drosophila-suzukii-matsumura/?cat=2025.
Sial, A. 2020. Organic management of spotted-wing drosophila (SWD) in small fruit production systems. Small Fruit News 20: https://smallfruits.org/2020/2007/organic-management-of-spotted-wing-drosophila-swd-in-small-fruit-production-systems/?cat=2025.
Vincent, C. I., M. E. García, D. T. Johnson, and C. R. Rom. 2010. Broad mite on primocane-fruiting blackberry in organic production in Arkansas. HortTechnology.