May 19, 2003 Volume 12 No. 10 Update on Pest Management and Crop Development
[Please note that we have included a predicted degree day accumulation for next week, based on temperature forecasts supplied by SkyBit, Inc. for Geneva, to our degree day table in Upcoming Pest Events. Using crop phenology and weather data that we have collected over the years, we have used this value to predict about where crops should be next week (in Geneva) in the Phenologies table.]
Phelps: 1st Codling Moth catch today, 5/19
Highland: 1st Codling Moth catch today, 5/19
(Dave Rosenberger, Plant Pathology, Highland)
Powdery mildew of apples is caused by the fungus Podosphaera leucotricha. Mildew can cause significant damage to many apple cultivars if trees are not protected with appropriate fungicides between tight cluster and first cover. Mildew infections on fruit cause russetting (Fig.1). Most fruit infections occur between pink and petal fall. Furthermore, effective control of mildew on leaves is almost impossible if fungicide protection is delayed beyond petal fall. The best mildew control occurs when mildewcide programs are initiated at the tight cluster or pink bud stage.
Powdery mildew overwinters as mycelia in infected buds. When buds begin growing in spring, the mycelia in the infected buds colonize the new leaf and shoot tissue as it grows (Fig.2). These "primary infections" become visible about the time trees reach tight cluster (Fig.3). The powdery white deposits on leaves with primary infections consist of mycelia and conidia (Fig.4). The conidia are wind-disseminated to new leaves where they cause secondary infections (Fig.5). (Secondary infections often begin appearing when trees are near petal fall, and they can become painfully obvious if trees are left unprotected until first cover. If left uncontrolled, the secondary infections colonize entire leaves along with the axillary or terminal buds that are formed during summer. Those infected buds then provide the inoculum for the next year.
Powdery mildew is often worse in years following mild winters and in years when the weather between bloom and petal fall is relatively dry with moderate temperatures. Winter temperatures below 10°F kill some of the overwintering mildew in buds, and temperatures of 10°F will eliminate 95% of overwintering mildew (Fig.6). Dry springs favor mildew because, unlike most other fungi, powdery mildew does not require rainfall or dew for spore germination. Mildew conidia can germinate when relative humidity is above 70% (as commonly occurs at night or during early morning). Rainfall actually decreases the severity of mildew, both because spores germinate poorly in water and because rains wash conidia off of leaves. Optimum temperatures for conidial germination and infection are 68-72° F, but infection occurs readily at any temperature between 50 and 77°F.
Apple cultivars differ significantly in their susceptibility to powdery mildew. Braeburn, Cortland, Gala, Ginger Gold, Gravenstein, Idared, Jonathan, Mutsu, Paulared, Rome Beauty are all highly susceptible to powdery mildew whereas Delicious, Empire, and Fuji are much more resistant. Cultivars such as McIntosh and Golden Delicious can develop severe levels of secondary infection when they are planted adjacent to a highly susceptible cultivar that supplies inoculum. Mildew-susceptible cultivars should be protected with fungicides that have activity against powdery mildew beginning no later than the pink bud stage. On more resistant cultivars, starting mildew control at petal fall may provide adequate control.
The SI fungicides (Rubigan, Nova, Procure) and the strobilurin fungicides (Flint, Sovran) are very effective for controlling mildew, whereas Captan, Polyram, and the mancozeb fungicides are not effective. Mildew in most orchards is probably resistant to Topsin M. The SI fungicides have both post-infection and protectant activity against mildew, whereas Sovran and Flint seem to work more as protectants. When mildew programs are initiated at tight cluster or pink and continued through first or second cover, the SI and strobilurin fungicides provide similar levels of disease control. However, if no mildewcide is applied until mid-bloom or petal fall, then an SI fungicide should be used as the first mildewcide spray because post-infection activity will be critical for rapidly shutting down further spread of the disease.
Sulfur is also effective for controlling mildew, but it has only protectant activity and is more easily removed by rain than are the SI and strobilurin fungicides. Sulfur at rates of 3-5 lb/A provides adequate suppression of mildew on less-susceptible cultivars or on highly susceptible cultivars where inoculum levels are low. In many orchards, however, at least two or three sprays of SI or strobilurin fungicides are needed to stop spread of mildew when trees are at peak susceptibility between bloom and first cover. Additional cover sprays with sulfur can then be used to protect new leaves until trees stop growing in late June or early July. Mildew can only infect young leaves for several days after they unfold, so susceptibility of trees to mildew drops off rapidly as terminal growth slows in early summer.
The bottom line on mildew control is to start the mildew program early (before bloom) and use at least three sprays of an SI or strobilurin fungicide before switching to less expensive alternatives such as sulfur. On mildew-susceptible cultivars, waiting until petal fall or first cover to apply the first mildewcide spray may result in unsatisfactory control and/or selection for fungicide-resistant strains of mildew.
(Bill Turechek, Plant Pathology, Geneva)
Blister spot, caused by the bacterium Pseudomonas syringae pv. papulans, is an important and difficult to control disease of apple fruit on 'Mutsu' (or 'Crispin'), 'Fuji' and a few less popular varieties. The disease can also infect apple foliage, leaf petioles, and shoot tips on a number of varieties, but these infections are considered important only in nursery production. The disease is generally most severe when temperatures are warm and rain and high relative humidity are prevalent during bloom and throughout the period of peak susceptibility (see below). However, infection can also occur under dry conditions. After this period, the level of susceptibility sharply declines. Most of the variability in disease is associated with weather conditions that affect growth rates of the apple.
Fruit are most susceptible to infection beginning two weeks after petal fall and become increasingly susceptible for another two to four weeks afterwards. The fruit are infected through the stomata and it is assumed that the leaves are infected in a similar manner. Most infections occur on the lower half of the apple. The first infections are observed as small darkened water-soaked areas, generally around stomata (eventually turning into lenticels). From there, small raised blisters are formed. The blisters at first start with a light color but eventually become purplish-black as they expand towards the end of the growing season. The epidermal layer covering the blister dies and will often flake off the surface. This stage is the most obvious sign of blister spot and can be mistaken for tiny lesions caused by apple scab. The lesions, which are generally circular although they can sometimes be lobed, rarely become larger than 4-5 mm in diameter. The infections are shallow, not extending more than 1-4 mm into the fruit flesh.
On leaves and shoots, lesions are a light tan to rust color, occurring on the under-surface of the leaves of shoots and spurs, and causing puckering and curling, generally misshaping them. Leaf symptoms can normally be found before those on the fruit.
Disease management: Applications of streptomycin (e.g., Agri-mycin 17 @ 8 oz/100gal) starting 2-2.5 weeks after petal fall and continuing for another 2 to 4 weeks is the standard program for control of blister spot. This program worked fairly well in New York until 1986, when resistant strains of the bacteria became prominent. Unlike fire blight, however, resistance is not a stable trait in the blister spot bacteria. In other words, resistance to streptomycin declines sharply in the absence of streptomycin. Therefore, growers can opt not to use streptomycin for a season when faced with loss of efficacy and then return to its use the following season and expect appreciable control. Fosetyl-Al (Aliette 80WDG @ 0.5-1 lb/100gal) is another option for managing blister spot. Like streptomycin, fosetyl-Al should be applied 10 to 14 days after petal fall, followed by two additional sprays at weekly intervals.
Currently, streptomycin and fosetyl-Al are the two best materials we have for managing blister spot. Both products will give about the same level of control when applied alone and at the appropriate timings. Slightly better control can be achieved if the two products are tank-mixed; this mixture may also be useful for resistance management. Unfortunately, the level of control can be quite variable. In years when disease pressure is high, you should expect less than 50% control with the most effective treatment. Alternative control options are somewhat limited. Two newer products with the potential for blister spot control are NutriPhyte Magnum and Oxidate. With NutriPhyte, you should expect about the same level of control as fosetyl-Al. My experience with Oxidate is limited and I have no feelings about what to expect from this product. Both products are currently being tested in trials here at Geneva.
Roundheaded Appletree Borer
Mullein Plant Bug
Oriental Fruit Moth
San Jose Scale
Spotted Tentiform Leafminer
White Apple Leafhopper
LIKE A PISTIL AFTER THE PETALS GO
(Art Agnello, Entomology, Geneva)
Having successfully negotiated our way almost entirely through what may have been the most typical early spring period we've seen in years, we should be about ready to consider the imminent petal fall pest management decisions while the pollinating activities are finishing up.
Adults move into orchards from overwintering sites in hedgerows or the edges of woods and adults are active when temperatures exceed 60 F. Adult females oviposit in fruit during both day and night but feed mostly at night. Depending on temperature, overwintering adults remain active for two to six weeks after petal fall. Because adults are not highly mobile, orchards near overwintering sites, woodlands, and hedgerows are most susceptible to attack. Fruit damage is usually most common in border rows next to sites where adults overwinter. Although initial post-bloom sprays for plum curculio control should begin at petal fall, growers are often unsure how many additional sprays will be necessary to maintain protective chemical residues to prevent subsequent damage throughout the PC oviposition cycle, which varies according to temperatures and weather patterns after petal fall.
Following from the fact that PC activity and oviposition are greatly affected by temperature, an oviposition model has been developed to determine when control sprays after petal fall are no longer necessary to protect fruit from PC damage. This model is based on the assumption that residues from control sprays after petal fall only need to be maintained on fruit and foliage until about 40% of the oviposition cycle is complete, which is predicted by the model to occur at 340 DD (base 50 F) after petal fall. Probably, this strategy works because, after 40% of PC oviposition is complete, adults usually are not moving into the orchard from outside sources, or moving around within orchards from tree to tree. Therefore, by this time, adults residing in treated trees have already been killed by insecticide residues and are unable to complete the remainder of their normal oviposition cycle.
In order to use this strategy: (1) Treat the entire orchard at petal fall with a broad spectrum insecticide. (2) Start calculating the accumulation of DD after petal fall (base 50 F). (3) No additional sprays are necessary whenever the date of accumulation of 340 DD falls within 10-14 days after a previous spray.
This primitive bee and wasp relative shows a preference for early or long-blooming varieties with a heavy set of fruit. This insect is generally a pest mainly in eastern N.Y., although it has been slowly making its presence known in the more western sites, including even Wayne Co. The adult sawfly emerges about the time apple trees come into bloom and lays eggs in the apple blossoms. Young larvae begin feeding just below the skin of the fruits, creating a spiral path usually around the calyx end. This early larval feeding will persist as a scar that is very visible at harvest. Following this feeding, the larva usually begins tunneling toward the seed cavity of the fruit or an adjacent fruit, which usually causes it to abort. As the larva feeds internally, it enlarges its exit hole, which is made highly conspicuous by a mass of wet, reddish-brown frass. The frass may drip onto adjacent fruits and leaves, giving them an unsightly appearance. The secondary feeding activity of a single sawfly larva can injure all the fruit in a cluster, causing stress on that fruit to abort during the traditional "June drop" period.
Certain insecticides that control these pests also adversely affect bees, which can pose a problem at petal fall because certain apple varieties lose their petals before others. In blocks of trees where petal fall has occurred on one variety but not the others, the variety that has lost its petals is likely to sustain some curculio or sawfly injury until the insecticide is applied. Two newly registered insecticides with activity against both plum curculio and sawfly, Avaunt and Actara, may have a slight advantage in this case. Although highly toxic to bees exposed to direct treatment, they are relatively non-toxic when dried. To minimize the hazard to honey bees, apply any pesticide only after ALL petals have fallen in the block and when no bees are actively foraging on blooming weeds (evening is better than early morning).
If you elected and were able to get a prebloom oil or miticide applied, fine. If not, and you are concerned about early buildup in certain problem blocks, Apollo and Savey are just as appropriate to consider at petal fall as is Agri-Mek, which we normally recommend at this time. Because of the cool temperatures up to this point, nymphal populations are likely to be small enough to be effectively handled by any one of these materials, if they fit into your product rotation schedule (i.e., weren't used last year).
Because these insects overwintered as 1st or 2nd stage larvae, they probably haven't had enough warm weather to encourage them to feed and grow as much by this time as they have in recent years, and may be somewhat smaller than they usually are by petal fall. This translates into potentially higher control efficacy with whatever product is used against them, as smaller larvae are generally easier to kill. Among the selective insecticides available, Confirm and B.t. products such as Dipel are options, and the latter can be used while blossoms are still present. Pyrethroids such as Asana, Danitol, or Warrior (see Chem News section, below) can also be effective, depending on past use history, but be aware of their broad-spectrum effects, which can work both for and against you, according to how many beneficial mites and insects you can afford to lose.
OFM has been receiving more attention recently, as we have been made increasingly aware of its ability to overcome some of the older OP-based control programs, particularly in peaches. However, now that we've made such a point of starting to consider control at petal fall instead of shuck split, this year has us once again seeing a flight that's just getting off the ground even though many peach orchards are certainly at (or past) petal fall. To maximize the efficacy of your 1st brood control, peach growers in western N.Y. at least could probably wait until the end of this week before starting a program such as Asana, backed up 10-14 days later. Refer to last week's issue for suggested management options in apples.
WALH nymphs can be numerous in some blocks, especially in the eastern part of the state. Besides Provado, Actara and Avaunt have proven to be effective against this pest, and a petal fall application of any of these materials also gives leafminer control. Furthermore, they will have an added effect on green aphid populations, which might otherwise be more problematic this spring, owing to the plentiful rainfall so far and subsequent availability of succulent green tissue. Rosy apple aphids can similarly be cleaned up with this strategy (using Actara or Provado only), although petal fall is often too late to prevent fruit damage that their feeding may have caused. Growers using Sevin in their thinning sprays will get some WALH control at the 1 lb rate. Alternative choices include Thiodan and Lannate; Agri-Mek or Carzol used for mites now will also do the job, but Carzol will be harmful to predator mites. The damage potential of this first generation should be evaluated carefully before deciding on the need for a specific control of this pest.
Last week, we were informed that the NYS DEC has granted a full state registration for the use of Warrior insecticide (EPA No. 100-1112) on all pome and stone fruits in New York. This pyrethroid product, manufactured by Syngenta Crop Protection, contains lambda-cyhalothrin as an active ingredient, and so represents a new class of pyrethroid products available for growers in their pest management programs. This should be a useful alternative for insect populations that have not been exposed to pyrethroids previously, as well as those still considered to be susceptible to pyrethroids in general. Warrior has good efficacy on a broad range of both direct and indirect insect pests of all tree fruit crops; it does not control phytophagous mites, and is toxic to honeybees as well as other beneficial arthropods. It has a 24 hour re-entry interval, and a PHI of 21 days on pome fruits, 14 days on stone fruits.Return to top