Virginian apple grower and stink bug survivalist Bill Mackintosh has some practical steps Aussie farmers can take to prepare for BMSB, should it breach the significant biosecurity measures in place to keep it out.
Bill addressed the APAL Grower R&D Update in Melbourne on Wednesday by videolink from the United States.
“You Australians will be in a better position with BMSB than we were in Virginia. You’re going into this with your eyes wide open.”
Bill Mackintosh was working as a consultant on Virginian orchards when he began to see a strange trend. From around 2001, fruit in the southern parts of the state was showing signs of what appeared to be a calcium deficiency, but something didn’t add up. “We just assumed fertility was out of whack; or something amiss in the balance of nutrition. But the injury was exactly the same in a light and heavy crop year – we were seeing what appeared to be calcium disorder on fruit even when the crop was big and the tree was vigorous.”
For Bill, this was enough to cause concern. “I was bringing fruit to the researchers at Virginia Tech for 8 to 10 years, but it was an uphill struggle – it took a long time to convince others that this wasn’t a calcium deficiency.” One client told Bill that if he didn’t figure out what the problem was soon, he’d be finished. “He was losing 40 per cent to 50 per cent of his pack out, and we still had no idea what was causing the injury”, Bill said. “We were really starting to worry.” Even when Bill began to suspect an insect, he never spotted BMSB during the day as they are mostly active at night-time.
Eventually, researchers at Virginia Tech realised that the BMSB was the culprit, and it has since become one of the most thoroughly-studied pests in the Mid-Atlantic area with a multi-million dollar federally funded research program.
Forewarned is forearmed, which is why APAL was eager to ask Bill for his tips for Australians preparing for and (one day) dealing with BMSB.
Be aware of the border effect
If your area isn’t attractive to BMSB, you may never have a problem.
In Washington State, says Bill, “They’re growing apples in a desert”. A lack of woodland around orchards means they rarely have a problem with BMSB, but if they do, they can control them with pesticides once, and they’re done. But in Virginia you can never control the BMSB population outside the orchard because the heavily-wooded state is full of plants that are attractive to stink bugs. “Whatever control measures you take in your orchard, they’re going to keep coming in if the woods are full of ailanthus and other attractive trees”, says Bill.
In the US, BMSB are attracted to tree of heaven or any ailanthus, locust trees, any legume such as soybeans or anything that has a pod. If you have any of these trees on your property, Bill recommends removing them. If they’re in the surrounding area but out of your control (on public land or on someone else’s property), you may not be able to have them removed but they can be useful as a way to find out if BMSB are in the area with the use of pheromone traps.
Stink bugs have a wide diet. The number of plant species they feed and complete their life cycle on has grown from around 200 to 300 species in recent years.
Without advocating cutting back on any particular variety of apples to reduce exposure to BMSB, Bill has some observations to share.
“Some varieties are more attractive than others. BMSB seem to like Pink Lady, while Fujis also show damage but not as much as Pink Lady. Earlier varieties like Gala don’t seem to be as affected, but this may not be due to the early pick – Red Delicious are picked only three to four weeks after Gala and they’ll have damage while Gala has none.”
If researchers can find out what it is about Galas that make them unattractive to BMSB, we may be able to impart that quality to other varieties.
Warmer winters will help BMSB thrive in Australia
Pesticides aside, the best defence against BMSB is a cold winter. Virginia obviously has colder average temperatures in winter than most of Australia’s growing regions, which means Australia is may not get the benefit of BMSB numbers dropping off in the colder months.
“We’ve had two cold winters below -17.80o Celsius recently, and saw a big dive in BMSB numbers”, Bill says. Typically, when temperatures drop stink bugs will start moving towards areas where they can overwinter and be protected. They’ll move to areas that are warm, such as wooded areas or the warmest side of a house where the sun hits in the afternoon. Bill notes that BMSB first arrived in the southern parts of Virginia, where they have warmer winters.
The Samurai Wasp
A very effective natural predator of BMSB is the Samurai Wasp, or Trissolcus japonicus. These pinhead-sized wasps destroy 60-90 per cent of stink bug eggs in Asia. Research is underway to release large numbers of Samurai Wasps in the US and Europe to protect crops, while New Zealand has pre-emptive approval from its Environmental Protection Authority to release the wasp to control BMSB if it is detected in NZ. Rigorous risk management processes in place around biological control agents to avoid a repeat of the cane toad experience, does not yet have a similar bio-control program plan in place for the Samurai Wasp, or alternative native predator.
Trapping for monitoring
The first step, says Bill, is just knowing that they’re there. “You don’t need to panic until you’ve actually seen them in the traps,” he said. In Virginia, growers use clear plastic fencing cut into squares and impregnated with a pheromone to draw BMSB in to count the population. Sticky traps in trees or pyramid traps are also effective for monitoring populations.
Bill personally hasn’t done any netting due to its cost, although he believes BMSB could be netted out.
If you have confirmed the presence of BMSB
Attract and kill
Once you do see proof of BMSB, one option for growers is to “attract and kill”, which is not yet happening on a commercial scale in the US. Bill explains: “It looks a bit like deer netting. We impregnate it with pyrethroid and use a pheromone to draw BMSB in. It works, but it’s still being fine tuned. Higher nets or screens up to 15 feet (4.5m) show a lot of promise … attract and kill may be commercially available by the time Australia has an issue with BMSB.”
BMSB are more resistant than other pests because their proboscis is long and thin, and goes right through the skin of the fruit, bypassing the pesticide. That being said, Bill has found the effectiveness of pesticides (some of which are available in the US but not Australia) to vary greatly in effectiveness*.
Not as effective
*Note: Opinions on the effectiveness of the above products are those of the interviewee, not APAL.
If BMSB arrives in Australia and is present in your orchard:
- Spring feeding from overwintering adults is confined to areas near their overwintering sites.
- During cell division, fruit can regenerate and overcome BMSB feeding injury, so it may not be necessary to spray until after cell division.
- Begin weekly monitoring no later than 40 days after petal fall and control measures 50 to 60 days after petal fall.
- If it looks like calcium deficiency, it may be BMSB, particularly if the crop is good or the tree is vigorous.
- Understand the sorts of plants and trees BMSB are attracted to and find out if you have these in your area.
- Some apple varieties are more attractive to BMSB.
- Mild Australian winters may not be cold enough to make an impact on BMSB numbers.
- The Samurai Wasp is an effective natural predator, but not present in Australia.
- Attract and monitor populations of BMSB with pheromone traps.
- Attract and kill BMSB with pyrethroid-impregnated screens.
Research the effectiveness of pesticides on BMSB before use.