Published: November 9, 2017

Several years ago I wrote an article urging expansion of blackberry production to meet market demand. Much has changed, however, in the past 5 years. Today I'm still a strong proponent of expanded blackberry production, though with several caveats. Let's take a look at the recent past, and discuss the practices that can help farmers realize blackberries as a viable and profitable option.

A major issue for blackberry farmers in Missouri is spotted wing drosophila (SWD), a devastating invasive insect pest first identified in Missouri in 2013. SWD larvae are present in ripe fruit at harvest, causing a rapid breakdown of fruit and loss of quality. By 2015 SWD was widespread in the state, and farmers now recognize this pest as among the greatest challenges to profitable blackberry production. In fact, all facets of blackberry production must focus on management of this pest if profitable production is to be realized. At present, primary management consists of properly timed insecticide sprays to protect the ripening fruit.

Blackberries showing leakage, the result of breakdown of SWD infested berries. Photo by Patrick Byers, at a farmers market in July 2015.

So what are the keys to successful and profitable blackberry production, in the face of SWD?

Gone are the days of marketing wild-harvested blackberries. Wild blackberries are a very attractive host plant for SWD, and wild harvested fruit will have high levels of infestation. Similarly, marketing fruit from minimally managed plantings is a risky proposition, as effective control of SWD requires system-wide attention to detail.

A positive development is the availability of early ripening thornless cultivars such as 'Natchez', 'Osage', and 'Ouachita' that offer large firm fruit that, if handled properly, can be transported and have a marketing window of 5-7 days. These cultivars ripen a portion of the crop in June and early July, before SWD numbers build to the high levels found later in the summer and fall. Lower numbers of adult SWD often equate to less pest pressure, which improves the effectiveness of the spray program.

Farmers should carefully consider the realities of primocane fruiting cultivars and SWD in Missouri. This type of blackberry ripens fruit from late July through frost. SWD numbers are high at this time, and excellent control is necessary to produce fruit suitable for marketing.

The benefits of trellising are many – separation of primocanes and floricanes, support to improve management efficiency, and with systems such as the rotating cross arm (RCA) trellis, the potential to overcome environmental risks (cold temperature damage to canes, solar injury to fruit). Of overriding interest today, however, is the need to develop a plant architecture that allows for effective coverage of fruit with protective insecticides. The RCA trellis, and to a lesser extent the V trellis, exposes the fruit on the outside of the plant, which allows for excellent spray coverage. The fruit on untrellised plants is buried within several layers of leaves and shoots, greatly reducing the effectiveness of insecticide sprays.

Organic blackberry production can be challenging in the face of SWD management. Two OMRI-approved insecticides are currently labeled for SWD, Entrust and Pyganic. Management of insecticide resistance with SWD requires using alternating sprays of insecticides with different modes of action. Unfortunately, while Entrust is quite effective as a SWD control, Pyganic is only rated as fair in controlling this pest. Thus, organic farmers do not have good options as far as an effective insecticide spray program.

SWD management extends to harvest and postharvest handling. Overripe fruit or fruit dropped on the ground is very attractive to SWD. Remove this fruit at harvest time, and destroy. Ripe fruit must be harvested promptly, and placed under refrigeration as soon as possible to destroy any eggs present on the berries. Farmers are urged to monitor for the presence of larvae in the fruit with a sugar or salt immersion test at each harvest.

Additional information on SWD management is available from Lincoln University's IPM program. The website http://www.lu-ipm.net/management.html includes information on SWD identification, monitoring, and management.