May 23, 2017
Widespread detections of San Jose scale in northwest Michigan tree fruit

 

Michigan State University Extension’s reports on San Jose scale’s arrival in northwest Michigan tree fruit.

“In past seasons, we have observed large populations of San Jose scale on sweet cherries in the northwest Michigan, and more recent reports show this pest is increasing in tree fruit crops in the state. Ten years ago, we were not able to readily identify San Jose scale damage in sweet cherry because sweet cherry branches and tree dieback were masked by ethephon damage due to hot and dry weather prior to harvest.

Additionally, San Jose scale had been deemed a key pest of apple trees and fruit and received little attention as a key pest of sweet cherry in Michigan since damage to cherry fruit was not documented in this state. Prior to the 2007 documentation of San Jose scale damage in sweet cherry trees, this type of San Jose scale epidemic had not been seen in Michigan.

Scales are insects with a unique life cycle that makes them difficult to control. Immature female and male scale overwinter underneath a waxy, turtle-like covering. When sap begins to run in spring, the overwintering scales grow and reach maturity in mid- to late May. At this time of the year, male scales come out from under the scale to mate with females. Females give birth to live young rather than laying eggs—these nymphs are the crawler stage of the life cycle.

Each female is capable of bearing 150-500 offspring. These crawlers start to suck sap with their needle-like mouthparts, and within three weeks, the crawlers molt and lose their old skins, legs and antennae to become a flattened sac with waxy caps. They remain attached to the trees with their mouthparts and protective covering. Weather permitting, immature scales will continue to feed, develop and mature, and depending on location, can have two to five generations. In northwest Michigan, there are typically two generations of San Jose scale.

San Jose scale feeds on sap of trees, and on healthy trees, large populations are needed to cause economic injury. Depending on the size of the population, San Jose scale can kill young trees in two to three years. Older trees can also be killed by scale, but they do withstand more feeding damage than young trees. In many cases, we have observed damage in older sweet cherries, and there is considerable dieback in the tops of the trees; in these situations, trees are not killed but the cropping potential is considerably reduced.

In addition to feeding on bark, San Jose scales can also feed on the fruit and leaves. Feeding on fruit causes bright red spots and is most commonly seen on apple. As mentioned previously, we have not identified San Jose scale feeding injury on sweet cherry fruit in Michigan.

Because these insects typically have two generations per year in our area, we have three optimal timings for control. An oil application during pre-bloom is highly effective for targeting adults by suffocating the overwintering scale. Insecticides applied mid-June and mid-August target crawlers before they produce their protective waxy covering. Targeting the first generation crawlers will prevent mating and reproduction, thereby minimizing the population of the second generation.

We conducted two San Jose scale trials in apples at the Michigan State University Trevor Nichols Research Center in Fennville, Michigan (Tables 1-4). The results of these trials will show the efficacy of the different scale materials, some of which are new insecticides. Growers can apply these results to sweet cherry as best they are able—unfortunately, we have not conducted replicated San Jose scale efficacy trials in sweet cherries. We intend to initiate these trials in 2018.

All treatments except those with Sivanto-alone provided significant levels of control compared to the untreated check (Table 2). Lorsban, Movento and Centaur treatments provided the highest level of control, but only the Centaur delayed-dormant and pink timings resulted in 100 percent clean fruit. The Environmental Protection Agency (EPA) re-registered the product Closer, but only post-bloom applications are permitted.

As a reminder, review all insecticide labels for additional information on restrictions for application, mixing, etc. From the 2016 data, the Sivanto (half green), Sivanto/Movento and Lorsban treatments all significantly reduced the incidence of San Jose scale injury to fruit (Table 4).

The results from both sets of data show that the tested materials provide good control of San Jose scale in apple. However, results were based on percent damaged fruit and number of scales per fruit; the number of scales or levels of damage to woody tissue were not measured.

It is possible San Jose scale may behave differently on apple and cherry. Hence, MSU Extension encourages consultants, scouts and growers to trap for males to better predict when crawlers will emerge to best time spray applications. Furthermore, be mindful that these chemistries have different mechanisms for their efficacy against San Jose scale. For example, products such as Lorsban (phytotoxic on sweet cherry foliage are not to be used past petal fall in tart cherry) and those that were not tested, but are recommended in the “2017 Michigan Fruit Management Guide” (ex. Warrior, Assail), are contact poisons that will have the best efficacy against crawlers if the spray material comes in contact with the pest.

The newer unique chemistries such as Sivanto and Movento are taken up by plant tissue and have different movement characteristics within the tree tissue. Sivanto displays translaminar movement and is xylem mobile, meaning the spray material will move in the foliage. On the other hand, Movento is phloem and xylem mobile, meaning this chemistry can move from foliage all the way to the tree’s roots. Because the tree takes up these materials, they are most effective against scale when the material is present in the tree prior to substantial feeding. Therefore, these materials should be applied prior to crawler emergence (roughly two weeks after peak male flight or petal fall timing).

Sivanto is not labeled for stone fruits, and Movento is labeled for pome and stone fruit. Lastly, Table 5 shows the speed of activity of the chemistries on the crawler stage and the potential for the insecticide to flare mites.”

Table 1. San Jose scale treatments for the 2013 San Jose scale efficacy trial conducted at the Trevor Nichols Research Center
Treatment # Treatment/

Formulation

Rate (product/acre) Application timing Spray date
1 Untreated Untreated Untreated Untreated
2

 

LORSBAN 75 WG 1 lb/a Delayed dormant April 30
Damoil 1 % v/v Delayed dormant April 30
3

 

Closer SC 3 fl oz/a Tight cluster May 6
R-11 0.125 % v/v Tight cluster May 6
4

 

Sivanto 200 SL 14 fl oz/a Tight cluster May 6
Damoil 1 % v/v Tight cluster May 6
5

 

Sivanto 200 SL 10.5 fl oz/a Bloom May 13
R-11 0.125 % v/v Bloom May 13
6

 

 

 

Sivanto 200 SL 10.5 fl oz/a Tight cluster May 6
Damoil 1 % v/v Tight cluster May 6
Movento 240 SC 6 fl oz/a Petal fall May 23
R-11 0.25 % v/v Petal fall May 23
7

 

Movento 240 SC 9 fl oz/a Petal fall May 23
R-11 0.25 % v/v Petal fall May 23
8

 

Centaur WDG 46 oz/a Delayed dormant April 30
Damoil 1 % v/v Delayed dormant April 30
9

 

Centaur 40SC 71.5 fl oz/a Delayed dormant April 30
Damoil 1 % v/v Delayed dormant April 30
10

 

Centaur WDG 46 oz/a Pink May 7
Damoil 1 % v/v Pink May 7
11

 

Centaur 40SC 71.5 fl oz/a Pink May 7
Damoil 1 % v/v Pink May 7

 

Table 2. 2013 San Jose scale efficacy results in apple from Trevor Nichols Research Center
Treatment # Treatment/ Formulation Rate (product/acre) Application timing Spray date Average # Scales / Fruit Oct. 3a % Fruit Infested Oct. 3 b
1 Untreated Untreated Untreated Untreated 1.0 ab 16.5 a
2

 

LORSBAN 75 WG 1 lb/a Delayed dormant April 30 0.2 cd 2.5 bcd
Damoil 1 % v/v Delayed dormant April 30
3

 

Closer SC 3 fl oz/a Tight cluster May 6 0.6 bcd 6.1 bc
R-11 0.125 % v/v Tight cluster May 6
4

 

Sivanto 200 SL 14 fl oz/a Tight cluster May 6 0.9 bc 9.0 ab
Damoil 1 % v/v Tight cluster May 6
5

 

Sivanto 200 SL 10.5 fl oz/a Bloom May 13 1.8 a 19.0 a
R-11 0.125 % v/v Bloom May 13
6

 

 

 

Sivanto 200 SL 10.5 fl oz/a Tight cluster May 6 0.2 cd 3.5 bcd
Damoil 1 % v/v Tight cluster May 6
Movento 240 SC 6 fl oz/a Petal fall May 23
R-11 0.25 % v/v Petal fall May 23
7

 

Movento 240 SC 9 fl oz/a Petal fall May 23 0.1 cd 1.5 cd
R-11 0.25 % v/v Petal fall May 23
8

 

Centaur WDG 46 oz/a Delayed dormant April 30 0.0 d 0.0 d
Damoil 1 % v/v Delayed dormant April 30
9

 

Centaur 40 SC 71.5 fl oz/a Delayed dormant April 30 0.0 d 1.0 cd
Damoil 1 % v/v Delayed dormant April 30
10

 

Centaur WDG 46 oz/a Pink May 7 0.0 d 0.5 cd
Damoil 1 % v/v Pink May 7
11

 

Centaur 40 SC 71.5 fl oz/a Pink May 7 0.0 d 0.0 d
Damoil 1 % v/v Pink May 7

Means followed by same letter do not significantly differ (P=0.05, Duncan’s New MRT)
ANOVA performed on square-root transformed data; data presented are actual counts.
b ANOVA performed on arcsine square-root transformed data; data presented are actual counts.

Table 3. San Jose scale treatments for the 2016 San Jose scale efficacy trial conducted at the Trevor Nichols Research Center
Treatment # Treatment/ formulation Rate (product/acre) Application timing Spray date
1 Untreated Untreated Untreated Untreated
2 Sivanto Prime SL 14 fl oz/a Half-inch green April 19
Damoil 90 EC 1 % v/v Half-inch green April 19
3 Sivanto Prime SL 14 fl oz/a Pink April 26
R-11 90 EC 0.125 % v/v Pink April 26
4 Movento 240 SC 9 fl oz/a Petal fall May 19
R-11 90 EC 0.250 % v/v Petal fall May 19
5 Sivanto Prime SL 14 fl oz/a Pink April 26
R-11 90 EC 0.125 % v/v Pink April 26
Movento 240 SC 9 fl oz/a 1C (CM bio+250DD) June 8
R-11 90 EC 0.250 % v/v 1C (CM bio+250DD) June 8
6 Lorsban Advanced EW 64 fl oz/a Half-inch green April 19
Damoil 90 EC 1 % v/v Half-inch green April 19

 

Table 4. 2013 San Jose scale efficacy results in apple from Trevor Nichols Research Center
Treatment # Treatment/ formulation Rate (product/acre) Application target Spray date San Jose scale

% damaged fruit

6/20/2016

1 Untreated  Untreated Untreated Untreated 7.3 a
2 Sivanto Prime SL 14 fl oz/a Half-inch green April 19 1.3 b

 

Damoil 90 EC 1 % v/v Half-inch green April 19
3 Sivanto Prime SL 14 fl oz/a Pink April 26 3.3 ab

 

R-11 90 EC 0.125 % v/v Pink April 26
4 Movento 240 SC 9 fl oz/a Petal fall May 19 2.5 ab

 

R-11 90 EC 0.250 % v/v Petal fall May 19
5 Sivanto Prime SL 14 fl oz/a Pink April 26 1.5 b

 

R-11 90 EC 0.125 % v/v Pink April 26
Movento 240 SC 9 fl oz/a 1C (CM bio+250DD) June 8
R-11 90 EC 0.250 % v/v 1C (CM bio+250DD) June 8
6 Lorsban Advanced EW 64 fl oz/a Half-inch green April 19 1.8 b

 

Damoil 90 EC 1 % v/v Half-inch green April 19

Means followed by same letter do not significantly differ (P=0.05, Tukey’s HSD)
ANOVA performed on square-root transformed data; data presented are actual counts

Table 5. Insecticidal activity on crawler stage of scale insects
Compound Labeled crops Speed of activity Mite flaring potential
Esteem All fruits Slow Low
Movento Pome and stone fruits Slow Low
Warrior/Asana Pome fruit (not on stone fruit label) Fast High
Assail (suppression only) Pome and stone fruits (not on blueberry label) Moderate Moderate
Sivanto Pome fruits (not on blueberry label) Moderate Low
Closer (suppression only) Pome and stone fruits Moderate Low
Centaur Pome and stone fruits Slow Low



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