On last week’s call, we decided to spend the whole hour with John Wise from MSU and save John’s weekly insect and disease updates for an addendum. And here it is!
You can download the MP3 of the addendum here.
Below is a full summary/transcript of the addendum.
0:00 – Follow-up on John Wiseâ€™s rainfastness discussion
In addition to my one comment about Dr. John Wiseâ€™s rainfastness reapplication chart, I would add that, in using his reapplication chart from a management standpoint, you can use your Codling moth trap counts and if you know when those CM flew into those traps during the week before the application as well as the time frame between the application and the rainfall. That calls into question your need to reapply, if you have CM counts before your application and then again before the rainfall. Oftentimes the numbers will drop off and you may actually not need to reapply depending on what the flight was in the interval between the application of whatever insecticide and the rainfall that has washed it off. It takes a little bit of management expertise, but itâ€™s possible to do that, and we have used those numbers to justify not reapplying.
1:45 â€“ Keep maintaining CM traps
Iâ€™d advise growers to continue to count and maintain their CM traps. At this point in the season, growers often stop counting their traps and stop cleaning them as frequently. This also is inadvisable because this is the time that CM can get a toehold in the orchard.Â If they are successful, their offspring will be flying late in August when nobody wants to be monitoring and applying insecticides in their orchards. So we donâ€™t want to let them get started this generation and then have to deal with their late offspring when weâ€™re starting the harvests. So, itâ€™s important to maintain your traps at least through 800 degree-days from your biofix.
3:10 – Apple maggot
Weâ€™ve spoken aboutÂ AM traps in the previous weeks. I just want to remind people that the use of red spheres or yellow sticky boards or a combination of the two â€“ those traps should be placed in the orchards if theyâ€™re not already there. I wonâ€™t go into the baiting and non-baiting using of AM traps, except to reiterate that the AM trap threshold for an un-baited red sphere is one female AM fly. For a baited red sphere, the threshold is 5. With the yellow sticky boards, it is one apple maggot. If you are going to use yellow sticky boards, you either need to replace them every 7 days, or you need to refresh their ammonium acetate attractant, the material that is used to attract the feeding females when they first emerge.
4:45 – Thinning & PC, Leaf miners, and Mites
If people are hand-thinning right now and they find some Plum curculio-damaged fruit, I would advise them to bag the PC-affected fruit and take it out of the orchard. Otherwise, if you drop them on the ground, it will allow the larvae to emerge from the fruit, go right into the soil, and pupate.
In terms of trap counts, we should start seeing some Red banded (leaf miner?). The second flight of Spotted tentiform leaf miner should also be flying right now in certain places, particularly if you had any first-generation mines.
You need stay on top of your mite counting. If you havenâ€™t had a problem with mites before now in the season, itâ€™s likely that you have some predators working those mite populations. The predators need to be maintained, but some of the materials that we use for controlling CM or PC can impact the predators, so you canâ€™t assume thatÂ the predators will stay on top of the European red mite population.
6:22 – San Jose scale
If youâ€™re caping limbs for crawlers, Iâ€™d just urge you to continue to change those tapes every 7 days, even if youâ€™re not actually looking at them. Preserve the tapes on a piece of paper, cardboard, or paperboard until someone like Peter or I can examine them for crawlers.
6:52 – Leaf hopper complex
There are Potato leaf hoppers and White apple leaf hoppers. We mentioned earlier in the season that there were differences between the timing of the adult appearance between the two species, makingÂ it easily to separate them. Right now, however, itâ€™s possible that we would see adults of both species out there at the same time. Itâ€™s difficult to tell the adults apart by looking at them. Rather than try to differentiate them by their appearance, look at the damage that they cause. So if you see the stippling â€“ the white dots or white speckles on leaves â€“ particularly on the inside of the canopy, that is evidence that you had White apple leaf hopper nymphs earlier. If the stippling has occurred already from first generation, itâ€™s likely that it will get far worse in the second generation. You may need to apply an insecticide to control the adults, or, later, the nymphs. White apple leaf hopper can cause economic damage on both bearing and non-bearing trees.
8:37 – Regarding Potato leaf hoppers: Â They will also have adults. But the adults are also going to be laying eggs, if they havenâ€™t already. The nymphs should be hatching out on the terminals (the growing points). This is primarily a problem for non-bearing trees because of the damage that it does to the growing shoots. It can stop growth and stunt the tree. I donâ€™t normally worry about Potato leaf hoppers on bearing trees. The adult Potato leaf hopper doesnâ€™t do that much damage to non-bearing trees; itâ€™s the nymphs that run around on the underside of the leaves on the tips of those shoots that do the most damage, by far. On non-bearing trees, therefore, youâ€™d want to control those nymphs before they get too numerous. On bearing trees, the only reason to worry about Potato leaf hopper adults or nymphs is if there are so many that they are producing large quantities of the honeydew they excrete. The honeydew will dot the leaves and fruit, and can look like flyspeck later in the season, as those droplets of sugar blacken with mold. So, if thereâ€™s too much of that honeydew and youâ€™re starting to see speckling, then sometimes even bearing trees need to have an application of insecticide.
12:44 – Borers
If you are concerned about clear-wing borers such as Dogwood borer or Lesser peach tree borer, and you are in the southern 2/3 of Wisconsin or even further south, then you will need to apply Lorsban this month to the trunks of the trees that are of concern. If you are concerned about borers and you are using OMRI-approved materials, obviously you know that you needed to do something before this because you needed to prevent the egg-laying instead of applying something like Lorsban that kills the new larvae as they hatch.
10:45 – Scab
To reiterate the fungicide situation: if you currently have scab in your orchard, whether itâ€™s on leaves, on fruit, or on both, I urge you NOT to apply anything that has any eradicant or kickback ability. So use NO single-site fungicides, like anything from the SI class or any of the strobilurins.
11:18 – Summer diseases
On cultivars with scab, you will not be able to apply strobilurins or SIs like Endar to control sooty blotch and flyspeck. The materials would control the sooty blotch and flyspeck, but they would also be exposed to the secondary conidia of the Apple scab and thus encourage rapid resistance development. If you have scab and you want to control sooty blotch and flyspeck, you just have to use other materials to which the scab has already become resistant. The main material that would fit under this category is Topsin M. For OMRI-approved orchards, the control is different, so Iâ€™m not going to go into that.
13:50 – Sooty blotch and Flyspeck
You should be counting up your leaf-wetness hours. I recommend that you use 175 leaf-wetness hours from your last fungicide applied after petal-fall that included a strobilurin or Endar/Topsin M. So, pick the date you last applied one of those two sets of fungicides, and add up your leaf-wetness hours from then â€“ all of them, NOT just ones that were 4 hours or longer. If you have not applied one of those materials post-petal-fall, you just start counting your leaf-wetness hours from petal-fall.
15:05 – Black rot / White rot
We should be about at the end of the heaviest sporulation period. If you do not have scab in your orchard and you are done spraying for Black rot and White rot, then you should be able to either extend your interval of fungicide protection, or reduce the rate of fungicide protectant, or both.
16:00 – Phosphorus acid fungicides (NOT phosphoric acid)
Aliette was the first fungicide of this group to be registered. There are now a number of fungicides in the group, like Agri-Fos, Phostrol, Prophyte, K-Phite. These fungicides are true systemic materials. That is, they are absorbed into the leaves and translocated up and down the xylem. These fungicides are short-lived. Even though they are the only fungicides we have that are translocated throughout the tree, they donâ€™t stick around for a long time. Consequently, they are not of great use as a protectant. However, they are registered for control of root rots (like Phytopthora) and Fire blight.
If you have a concern about your trees having wet feet or having problems with Phytopthora growing on those roots (which would be more of a problem on smaller rootstocks), this is the one material that you can use prophylactically. It is normally applied twice, about six weeks apart. The first application is usually done about now, and the second one happens in the first part of August.
If Phytopthora is not a problem, but you are seeing some Fire blight (particularly the Shoot blight form of Fire blight), then you may want to try using one of this group of fungicides to reduce the amount of bacteria in the treeâ€™s system. It wonâ€™t necessarily stop the Fire blight or change the symptoms, but it may reduce the amount of bacteria reproduction and the formation of cankers.
I would also recommend that you consider using one of these fungicides in orchards that suffer hail damage at this time of the year, particularly if the hail breaks open soft woody tissues (1st-year growth). If that 1st-year growth is broken or cut open by hail, Black rot and White rot infections can enter the tree. This fungicide group may be of some utility. Itâ€™s the only option we have to (possibly) reduce the amount of Black rot and White rot that affects those trees in the following years.
Again, remember: they are not protectants.