The use of drop sheets in macadamias

In this AMS podcast, Leoni Kojetin from the Australian Macadamia Society, talks to Dr Karina Griffin, plant pathologist and crop protection consultant with the AMS and Chris Fuller, plant protection and orchard management consultant and grower liaison officer, about the evolution of integrated pest management and the use of drop sheets as a monitoring technique. 

Listen in to find out why understanding exactly what’s in your orchard at a specific point in time will lead to a more informed IPM program and better outcomes for your orchard. Learn why some traditional monitoring techniques are no longer working and how to implement drop sheet monitoring in your orchard.

Chris has a long background in the macadamia industry and is well known to growers, especially in Queensland, and Karina has been involved in crop protection and evaluation trials looking at efficacy of different crop protection options. 


Leoni. Today we are with Chris Fuller, plant protection and orchard management consultant and grower liaison officer. And we're also with Dr. Karina Griffin, the AMS's resident plant pathologist, crop protection and plant health consultant.

Today we're talking about integrated pest management, but in particular, we're talking about some of the new monitoring techniques that growers can employ. We've heard a lot about drop sheets and how they can help us in understanding exactly what's in the orchard.

So, Chris and Karina, tell us a bit about your background in the macadamia industry and how IPM has evolved in your time.

Chris. I came out of ag college and got my first job with Ian and Jan McConachie working in their nursery at Wolvi. I then started working in the business in managing the orchards Ian had with his company, Australian Macadamia Management, which Tim Salmon was a part of in the early years as well. I worked under Tim, which was fantastic. And I started my job driving around in my old Ford Laser, looking for bugs back in the early ‘90s.

Karina. I've worked in various research and development roles in the industry, mostly focused on plant health and crop protection, initially in vegetable crops. Now I'm in the macadamia industry it’s a lot nicer simply because, working under trees, you don't have to crouch down, rather you get to stand and look at things.

Leoni. Chris, how has integrated pest management (IPM) evolved in macadamias over the last few decades?

Chris.  IPM involves using cultural, biological, and chemical controls, which we know are all necessary to grow our crops at the moment. Monitoring is the cornerstone of IPM because it gives us the information to make our management decisions. Depending on what we find through monitoring, we can decide whether a cultural, biological or chemical control is needed.

Leoni. Karina, I'm sure you see a lot of differences every season with changing environmental conditions affecting the pest profile that growers must manage. This underpins why monitoring is so important.

Karina. Climatic factors such as temperature, humidity and rainfall affect different pests in different ways. In all the crops that I've worked in, you have the core families that affect all crops. While I started in vegetables, I have found that a lot of principles apply to macadamias.

Leoni. Let's talk about drop sheets, which are creating a lot of interest as a way of helping understand exactly what's in the orchard at a specific point in time.

Chris. Monitoring with drop sheets has been around in different forms for a number of years now. I actually got into the industry to help growers reduce their chemical use whilst maintaining a good quality crop for harvest.

Traditional advice is to do a late spray round “just in case” but I wanted to test this so under half a dozen trees through the orchard, we put down the sheets and ran the spray rig past using a traditional chemical product. Then we came back to have a look, and the only thing that we dropped out on those sheets was a couple of assassin bugs.

I'm not advocating that there are not pests doing damage in what we traditionally call late in the season. Rather, what I like to do before advising on a response is to find out what is there and whether it is necessary to take steps to manage it. Just pulling the trigger in January or February is not really the right way to go about it. Using drop sheets to find out definitively what's there means you can decide based on what you're seeing.

Leoni. What are some of the difficulties with understanding pest profile and pest pressure in the late part of the season?

Chris. One of the things we know is that spotting bug can be doing different things depending on whether it is early, in the middle of, or late in the season. It's not just nuts they feed on, rather we believe that they can be feeding on shoots and other parts of the tree. The fact that you may have some spotting bug around late in the season doesn't automatically mean it's a threshold for spraying. If it's a certain time of year and we believe they're not doing commercial damage and, at the same time, populations of beneficial predatory bugs are building up, we need to consider whether we could be upsetting the balance for the start of next season by doing unnecessary late sprays. One thing I'm hoping we learn as more people adopt this technique is to understand what's happening through the off season and what it means.

Leoni. Karina, can you tell us how applying any sort of plant protection application can disrupt orchard management?

Karina. Different chemistries have different impacts. A lot of current products and those in the pipeline are very target-specific for pests and have minimal impact on a lot of the biodiversity in the orchards.

This means that the choice of product is important as it determines what impact you have on the orchard system, for instance whether you're killing just the bad guys or the good guys as well. Often, growers and consultants are looking for the bad ones, but in the orchard there is a massive proportion of good guys working for you rather than against you.

Of course, it's hard not to be focused on the pests and the ones that are causing you damage, because they obviously are the most economically detrimental to your system and profitability, but a high proportion of insects are actually not causing any damage at all. They might just be feeding on sap and nectar and pollen, or they're feeding on pests, or they're just using it as a little home and then they might feed on the ground.

Leoni. Chris, that's exactly what a drop sheet does; it's a visual representation of what's there, and the impact that you're having with that application.

Chris. I touched on the use of drop sheets when looking at late season bugs, but there are other reasons that I use them. As an example, at the start of what is traditionally our spraying season, say, after we have done our flower sprays for the pests and are coming to perhaps that first husk spot spray round. This is when growers are trying to work out whether there are pests around at this time of year and whether they need to add an insecticide to that first fungicide round.

By putting a drop sheet down and spraying a few sample trees to identify whether there is spotting bug very early in the season (around early October), that physical evidence can be used to decide whether to add an insecticide. Spotting bug is our biggest pest and it is important to keep it out from October right through to February. Starting early with monitoring and control measures mean a hell of a lot less build up through the traditional spotting bug season.

Another reason I use drop sheets was mentioned by Karina. When a new product is introduced, a lot of growers aren't comfortable with jumping straight in and using it, especially if it's very expensive; they generally hold off and wait to see what someone else's experience is. Using a drop sheet to identify the impact of a new product is something I have done for spotting bug. The product was registered to be softer on the beneficials and the other biota in the trees, so I tested this by first spraying the product and seeing what comes down.

Then I would go back a few days later and hit those same trees with a more traditional product, e.g., Bulldock, and have a look at what else comes out of the tree. The first time I did this after that follow-up spray with Bulldock, I didn't bring down any more spotting bug, but I brought down a heap of bycatch such as spiders and praying mantis. This showed the grower the efficacy of the new product and he was very happy with what he saw.  He believed in the benefits of having those beneficials left within the orchard, and is still using the product to this day.

Leoni. Chris, what would you use generally on a representative tree to do a drop sheet test for a larger part of the orchard?

Chris. When I'm doing drop sheet testing, I hand spray trees using a backpack sprayer modified with a handgun and a natural pyrethrum for a knockdown. From experience, this will kill the pests. I’ve sprayed trees with natural pyrethrum that I know spotting bug or leptocoris are in because I see them or their damage and am able to see them on the sheets after spraying. 

The grower can also use just whatever product they would normally use and you can do it in a spray rig if you want.  

Leoni. Does tree size affect this, Karina, for instance, if you have very tall trees you could do a one-sided spray?

Karina. Yes. The backpack sprayers we have now have pretty good reach, for example the one that Chris has reaches a good ten metres. With big, old plantations, growers could use their airblast sprayers to run along the row as long as they know they are getting the coverage.

Chris. The 20 L backpack I'm using now puts out about 7 L a minute at a pressure of 30 bar, so it is actually hosing it on, and I can get two trees done quite quickly, I spray about 10 L a tree. Spraying the trees doesn't take long, and you can get good coverage.

Leoni. What about the type of material to use for drop sheets?

Chris. I've tried many different types of material over the years. I used to use Bunnings’ paint drop sheets, which were great to start with, but the chemical would pool in them and they'd flap around and blow off the pests. I've also tried different-coloured shade cloth. I've now settled on high density polyethylene insect exclusion netting which has, I think, 1 mm gaps.

It stays on the ground without being pegged down, which means I can run it out quite quickly. I've cut a keyhole in it, so it's one piece. It covers the whole shadow or canopy line of the tree, and with the folding technique I’ve developed, it takes me no more than probably two minutes to lay it down. Because it's perforated, the chemical flows through it, and the insects show up really well on the creamy, white color.

Leoni. What's the reaction from growers when they see what drops out of the tree?

Chris. At certain times of year, there is an incredible amount of insect and biota activity in a tree. Sometimes, when you see the amount of bykill coming down under a tree, it's amazing. Often there are insects there and I've got no idea what they are. We obviously know our target pests and the ones in our guides, but there are other things in there that are obviously doing something. If we see a few of our target pests on the drop sheet, but a lot of other things in there, what I want to know is what they are all doing. How does that interaction work within the tree?

And this is something James Thomas has often brought up. If we drop one spotting bug and a hundred parasitic wasps, where's the balance there? Or a hundred, probably more, spiders? It would make you cry how many times you see spiders on the drop sheets, and praying mantids, and similar beneficials. We've got photos of spiders killing spotting bugs. Growers often ask about what these insects are doing and how they interact, and some of the time I don't have the answers, but hopefully, as drop sheeting becomes more common, we'll be able to answer some of these questions.

Leoni. Karina, is a grower’s entomological knowledge a limiting factor for drop sheeting?

Karina. Growers can definitely drop sheet by themselves if they've got the experience and the entomological knowledge, and we know that a lot of the bigger companies are employing their own agronomists. But, as Chris was saying, even if you do have that knowledge there are some things you just look at it and you're like, “I don't know what that is”. Know your pests and know your good guys.

Leoni. And from a cursory look, sometimes things can look like a pest, but perhaps not be?

Chris. Exactly, that's right, Leoni. I've dropped one pest last season, which I was sure it looked like some sort of spined citrus bug, but through further investigation turns out it was actually a spined predatory bug. So these are the interactions, like I said, we really need to find out.

Leoni. Could the future for drop sheeting include the implementation of drones, Karina?

Karina. Absolutely. We're starting to see commercial operators for drone spraying in macadamia orchard systems, and I think that's going to become more common. The feedback from some of the growers and consultants is very positive, so drones will definitely be more prevalent.

Leoni. And we're not talking about swarms of drones applying product to whole orchard, rather we're talking about scattered drones?

Karina. Yes, you can do hotspot management easily. Commercial operators often have a few drones, and they're just constantly changing over their tanks, which are small so limited in the amount that they can carry. Despite this, I think they can get to a point where they're almost as quick as sprayers if they get their rotations right and they have premixed chemicals ready to go.

Leoni. Chris, how do you think growers can start to build their confidence in the results from a drop sheet to make an informed orchard decision?

Chris. When you are spraying a tree well and you are dropping what you believe is everything out of that tree, the proof is in the pudding. We know that some of the traditional monitoring techniques are not working anymore. Let's say, for example, we're trying to monitor for spotting bug and we're relying on fallen nut as an indicator, which is the usual method. We know that as we're having more dry years, the trees aren't shedding stung nut as late into the season as they were, so this method is becoming less accurate. The fact that you are not seeing drop stung nut does not mean anymore that spotting bug is not in your tree.

I think we've got to implement drop sheeting from, say, the end of October to give a more accurate reflection of what is in the trees. The other option, which leads on to another use for the drop sheeting, is going through after one of your commercial spray rounds. A couple of days later go in and hand spray a tree very heavily. If you're dropping pests out still, you know there's probably a problem with your calibration and your coverage.

Another thing, let's say, for example, we're leading into December and we've got drier years now, and we've got emerging pests like leptocoris, which shows up in some areas in some years and seems to be becoming a bit more widespread. What we're seeing now as we're doing more drop sheeting is that it is actually around in a lot more years than we think, and in wetter years than we think. And the reason we need to know if it's showed up at your orchard, say in December, is that is when people traditionally apply Bulldock. Unfortunately, Bulldock is not effective on leptocoris. So, if you drop leptocoris on drop sheets in early December it can change the chemical you need to use for that spray round.

Leoni. Karina, we've seen growers who have used drop sheets significantly reduce the number of pesticide applications because they're only treating the orchard when there's something there to spray for.

Karina. Yes, that's right, and it all comes down to monitoring. As Chris was saying, monitoring is the key to being able to reduce pesticide use. And that can also be a challenge as we know there are areas in the macadamia industry where it's hard to get pest monitors into your farm. Because of that, growers are having to go back to a bit of calendar spraying.

This means we have a skills gap there, which is something that we should acknowledge, because if you don't have skilled people helping you monitor or do drop sheets, then it's really hard to make informed decisions. This is particularly important because a lot of the chemistry we've got now, and that is coming out, relies on applying it when the bug is at a certain part of its life stage to kill it. So, understanding not only that you've got the pests there, but what part of its life cycle it's in is also important. And that's where monitoring is crucial.

Leoni. As you say, a lot of the new chemistry has a very tight window for timing, so it's even more essential for us to know that the pest is there.

Karina. Yes, absolutely. And they're also moving to products with a shorter period of residual activity, which makes them a bit safer for some of your off-target insects and biota, but shorter residual time then means that you're not getting say three weeks’ worth of control out of a product for one pest. So, timing is critical.

Leoni. To round up, we know that Australia has an advantage in the global market because of our food safety record and because of our sustainability record, and that often gets us a higher value and preference in markets. But what do you think is ahead for us in IPM in macadamias, Chris?

Chris. I don't think that the macadamia industry is a particularly high spray user now. If we can pull that back, even remove one or two rounds from our current spray program, I think we really can promote ourselves strongly as a green industry.

Hopefully, we'll be investigating more biologicals, which we might find through drop sheeting. We might identify pests and work out what they're doing. We could implement robotic identification of insects. We spray with drones to replace the feet on the ground because it is a big and developing industry, and as we said, we need data. Data needs to be collected through feet on the ground because without that people have to make broad recommendations.

Leoni. Well, thanks so much for your time today. You both are great examples of two people who are trying to find newer, innovative ways that we can deliver our crop to our consumer while being good stewards of the land. Thank you so much for your time.



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