Posts Tagged ‘wild blueberries’

Spotted Wing Drosophila (SWD) July 25, 2013

Thursday, July 25th, 2013

More SWD have been captured in the Downeast growing area on the blueberry barrens. Male SWD were caught and confirmed in a few locations. At the University of Maine Blueberry Hill Farm SWD have been caught in more locations throughout the fields there. So far our fruit sampling (several fields sampled yesterday) has not revealed any SWD larvae in the fruit, but the recent capture of male SWD suggests that reproduction of this pest in blueberry fruit may have commenced. If you are capturing male SWD consider protecting the crop until harvest.

Blueberry fruit fly (BFF) appears to be in high densities in many locations throughout the state. Do not forget about monitoring and managing for this significant pest. Some fields have noticeable BFF attack in their fields demonstrated by considerable shrunken berries.    

Again, as stated earlier in the week, we recommend that you continue to be vigilant and monitor for BOTH SWD and BFF. Be prepared to protect your crop if SWD trap captures occur. Again, hopefully a significant amount of harvest can occur prior to SWD captures in some fields.

Spotted Wing Drosophila (SWD) July 22, 2013

Tuesday, July 23rd, 2013

More SWD have been captured in the coastal growing area. Nine flies were captured this past week in a Warren field and continued single SWD detections have been found in Union and Lincolnville. However, despite the number of fields where this pest has been captured in traps there are still SEVERAL fields in this area that have not detected SWD. The first capture Downeast was in Marshfield last week, but as of today no other occurrences have been reported. It APPEARS that recent applications of insecticide to control blueberry maggot fly might be negatively affecting SWD as fields that we had found SWD in earlier and that were sprayed have had few if any subsequent captures. This is just a guess, because it could also be that the hot weather we had last week was detrimental to SWD as well. It has been reported that SWD does not tolerate extremely high temperatures.

Last week we collected fruit samples from coastal and central Maine and inspected the fruit for SWD larvae infestation using the “salt water crush test”. The fields sampled were fields that have had SWD reported in them for at least a week. Thus far, we have not found any SWD larvae in fruit, but we will sample more fields this week.

At this point we recommend that you continue to be vigilant and monitor. Be prepared to protect your crop if SWD trap captures occur. Again, hopefully a significant amount of harvest can occur prior to SWD captures in many fields.

NOTE: SWD updates will only be made when we have trap captures.

Valdensinia leaf spot

Tuesday, July 16th, 2013

Now is the time to look for Valdensinia leaf spot in your fields.  The wet weather conditions we have had over the last month will have caused many cycles of spore production and infection if you have this fungus in your field.  I have seen a new field with Valdensinia leaf spot in Ellsworth.  Areas we have often found it are along the edges of roads, in wet areas in the field and areas that are shaded by trees along the field edges.

Do NOT scout your field when the plants or ground is wet.  This may move infected leaves  around your field. 

Symptoms are large brown leaf spots that are rounded with dark margins compared to the inside of the lesion.  On the underside of the lesion, you will see a dark spot with a hand lens, or sometimes the naked eye, which is the spore still attached to the leaf.  Lower leaves, particularly in prune fields, will be falling off by now.  Upper leaves, particularly in crop fields, may have many spots and may still be attached. 

If you think you have Valdensinia leaf spot, please contact Seanna Annis at sannis@maine.edu or the blueberry hotline 800-897-0757 (in Maine only).

lowbush blueberry stems with missing leaves and leaves showing Valdensinia leaf spot symptoms     Picture of leaves with Valdensinia leaf spot lesions

 

Spotted Wing Drosophila (SWD) July 8, 2013

Monday, July 8th, 2013

It is no wonder with this HOT weather over the 4th and following weekend a few more SWD captures have surfaced since my update on July 2nd.  However, last week’s capture of a male SWD in Cherryfield was a misdiagnosis. When we looked at it, two spots were found on each wing and so we have NOT had a recent SWD capture Downeast yet. But, in the south…male SWD were captured in Dresden and Whitefield on July 3rd in the southern coastal blueberry-growing region. On Saturday, July 6th, I found a male SWD in a Winterport blueberry field. I have deployed 20 traps in this field and only ONE trap had an SWD. I also have 25 traps deployed in a Stockton Springs field, but as of yet no male SWD have been identified and I have not had a chance to go through all the traps for microscopic detection of females yet.  I am guessing that from the low number of captures that SWD has not completed its first generation, producing new adults.

An important and timely question…What shall I do if I detect male SWD in traps in my field at this time of year (early July)?  I think the thing to first state is that if you have only a slight proportion of ripe (blue) berries (< 0.5 % or so) then don’t panic. At this point I believe ONLY the overwintererd SWD are in our fields as of yet and SWD needs RIPE fruit to lay eggs in. However, they will attack these fruit and start to build in numbers over the next several weeks. So, there is a trade-off between: 1) starting to protect your crop too early with insecticides and having to spray many times prior to harvest and 2) incurring damage and fruit loss. Each grower has to strategize to solve this dilemma of whether to take action or not.

ONE WAY of finding a solution to this problem is to determine at what percent of ripe fruit in your field is the trigger for action.  As an example…If you typically get 2,500 lbs / acre on a given field and guessing on past prices you can estimate what you will get for your crop…then you can calculate how much loss in revenue you will incur if SWD takes 1, 2, 5, 7%, etc., of your crop and you can determine what the economic threshold would be…or in other words the cost of crop loss that will equal the cost of controlling SWD (application + insecticide cost). So, in our example if you normally get $0.75 / lb, then 1, 2, 5, and 7% infestation EARLY in the season will cost you…25, 50, 125, or 175 lbs / acre or in dollars…$18.75, $37.50, $93.75, or $131.25…in this case if it costs you $100/acre to treat the crop then somewhere between 5 – 6% crop loss would be your decision making trigger to treat, meaning 5 – 6% of your crop being ripe.

The calculation above is ONLY a guide. Growers are different in their aversion to risk and price that they receive and so it is not possible to give a simple one answer that fits all.  BUT, this being said another thing you might want to consider prior to an insecticide application is to take a known sample of ripe fruit from your field (small collections from several locations throughout field). Place a quart of your fruit in a gallon zip-lock baggie and mix a salt solution of 1/4 cup salt to 4 cups water.  Lightly crush the berries in a bag and add the salt solution.  Allow the fruit to sink to the bottom of the bag and wait approximately 10-15 min.  Several baggies can be easily set up if you want to sample more than 1 quart of fruit. If the fruit is infested, the larvae should float in the solution for you to visually inspect (See my SWD factsheet showing what larvae look like).  NOW you have a better idea of crop loss that exists at the time of sampling.

The last aspect of EARLY SWD management that I want to bring to your attention comes from my inspection of blueberry fruit fly traps this past Sunday in the field. I was at a field in Stockton Springs and the threshold (10 cumulative flies / trap) was already surpassed at 13 flies / trap. So, if this grower is thinking about a perimeter spray (a location where we also tend to capture lots of SWD)…then an insecticide that is ALSO effective against SWD would be a logical choice. An insecticide that would NOT a choice is imidacloprid (ADMIRETM, PROVADOTM, MONTANATM, PREYTM, etc.) since efficacy against SWD is low. Reduction of SWD adult numbers as a result of a perimeter blueberry fruit fly application might buy you some more time before you need to manage for SWD or maybe even allow you to harvest early making an insecticide treatment specifically for SWD not necessary. However, at this point we do not know how this might play out and so it is no guarantee that spraying for blueberry fruit fly will have any effect on SWD.

*A NOTE…for organic growers the above points are also relevant. Insecticide options are EntrustTM or PyganicTM. The capture of SWD may also be a trigger for deploying exclusion netting over your crop or for deploying a grid of bait cups (every 25 ft) throughout exceptionally high yield areas of your field as a trapping out tactic.      

NOTE: SWD updates will only be made when we have trap captures.

Spotted Wing Drosophila Update for July 3, 2013

Wednesday, July 3rd, 2013

Dave Yarborough and Frank Drummond will be sending out SWD updates 1-2 times a week over the growing season. Frank and Judy Collins will be monitoring 18 field sites from Stockton Springs up to Jonesboro. Dr. Jim Dill and Dr. Dave Handley (UMaine Cooperative Extension) are monitoring traps in mid-coast to southern Maine in strawberry, highbush blueberry, and raspberry fields. In addition, we will be in contact with several growers from the coastal region. Therefore, we should have a good monitoring network this year!

July 2 update: Many growers have traps out now. I have not verified ANY SWD captures at this point. Very early in the season (May) an individual SWD was captured Downeast, but this was part of the overwintered population still in hibernation. I have verified at “look-alikes” to the SWD in southern, coastal, and Downeast Maine, but again as I stated NO CONFIRMED SWD HAS BEEN CAPTURED IN MAINE AS OF TODAY. This morning I received an email from a grower in Cherryfield that stated they caught a male SWD in their strawberry field. I will be checking this out to verify the capture shortly and let you know next week. 

In the meantime, don’t forget about the blueberry larvae (BFF) threat. Get your traps out for them also. BFF was trapped last in Waldoboro, Maine last week. No need to panic as they have just started emerging in the coastal area AND adult females need 7-10 days of warm weather before they are capable of laying eggs in to RIPE fruit (which is only starting to appear in noticeable proportions in the coastal region.  

NOTE: SWD updates will only be made when we have trap captures.