3. Leaf pests

Leaf pests can be divided into two main groups, sucking pests and chewing pests. Sucking pests include twospotted spider mites, cyclamen mites, chili thrips, aphids, whiteflies, potato leaf hoppers, and spittlebugs. Chewing pests include armyworms, cutworms, and strawberry leafrollers. Injury to leaves reduces the plants ability to photosynthesize (make food), which can reduce the quality and quantity of fruit produced. In perennial production, this injury can affect the yield the following season, also [3].

#### 3.1 Twospotted spider mite

Twospotted spider mites,Tetranychus urticae Koch (Figure 1) are oval shaped and tiny. The adults are 0.5 mm in length, which is about the size of a period in 12 point font. They are usually light greenish-yellow in color with two large, dark spots on their abdomens. However, brown, red, orange, and darker green forms also occur. The eggs are spherical and clear to tan in color. The eggs and all stages of mites are usually found on the undersides of leaves. The twospotted spider mite life cycle progresses through five stages: egg, six-legged larvae, protonymph, deutonymph, and adult. Each of the three intermediate stages feeds and grows for

#### Figure 1.

Twospotted spider mites and eggs on the underside of a strawberry leaf as seen under a microscope (photo credit: L. Buss, UF).

only a short time before entering a resting state prior to molting to the next stage [4]. Females are larger and rounder than males. Development from egg to mature adult takes an average of 19 days, although this time can be as short as 5 days [4]. Optimal conditions for development are high temperatures (up to 38°C) and low humidity [5, 6].

sometimes on large fields but this assessment method has some limitations and a history of mite population in the field is sometimes needed to improve its accuracy. A common threshold for this type of monitoring is 5% of leaves infested. In California, the treatment threshold is an average of 5 mites per leaf before the harvest period begins, which increases to an average of 15–20 mites per leaf once the harvest period begins [7]. An average of 10 spider mites per leaf is a common

Management of Strawberry Insect and Mite Pests in Greenhouse and Field Crops

There are a number of miticides available for twospotted spider mite management. Thorough spray coverage is essential for effective applications [3]. Rotating modes of action is also very important as spider mites can quickly develop resis-

There are several commercially available predatory mite species that can be used in a twospotted spider mite management program [3]. They are especially effective in greenhouse settings. Neoseiulus californicus (McGregor) and Phytoseiulus persimilis Athias-Henriot are two commonly used species [9, 10]. Neoseiulus californicus mites (Figure 3) are orange to peach in color and slightly larger than twospotted spider mites. Their eggs are milky white and ovoid in shape. They prefer spider mites as prey and can subsist on other food sources, such as small insects and pollen, when twospotted spider mite numbers are low. For this reason, preventative releases of small numbers of N. californicus early in the season can reduce the severity of mite

outbreaks and even eliminate them all together in some cases. In contrast,

P. persimilis mites (Figure 4) specialize on spider mites, so their population declines rapidly once the spider mite population has declined to low levels. This can necessitate multiple releases in a season. Adults are pink in color with spider-like legs. Eggs are similar in shape to N. californicus eggs and have a pinkish to orangish tint. Preventative and curative rates are listed on supplier websites. If spider mite numbers are high, it is advisable to knock down the population with a miticide before predatory mites are released. Predatory mites should be released 7–10 days after the

Cyclamen mites, Phytonemus pallidus (Banks), are half the size of spider mites, 0.25 mm, and invisible to the naked eye [3, 7]. Adults are shiny and pinkish to orangish in color while immatures are opaque white. Eggs are ovoid and translucent. They feed on developing tissues and are most commonly found on unfolded

N. californicus mite and eggs on a strawberry leaf (photo credit: E.M. Rhodes, UF).

threshold used in Florida production [8].

DOI: http://dx.doi.org/10.5772/intechopen.82069

tance to miticides due to their short life cycle.

miticide application.

3.2 Cyclamen mite

Figure 3.

105

During feeding, twospotted spider mites puncture leaf cells and suck out their contents [3]. The feeding injury causes affected leaves to have a stippled appearance (Figure 2a and b). Spider mites do produce webbing, which is where their common name originates from (Figure 2c). The webbing provides protection from predators and may also help maintain favorable temperature and humidity conditions for the mites. Webbing is only visible when populations are high and, therefore, economic damage to the crop is already occurring.

Monitoring can be accomplished by checking and counting twospotted spider mites on the underside of strawberry leaves with a 10x hand lens [3]. Alternatively, strawberry leaves can be collected from the field and examined later. Leaf samples should be processed within 3 days of collection if possible. In annual production, sampling for twospotted spider mites should begin after the transplants have become established. In perennial culture, sampling should start once the new leaves fully open in the Spring. Sample 13–25 fully mature leaves per hectare. Counting the number of spider mites on each leaf will give more accurate results, but it can be time consuming. An alternative is simply to note how many leaves have spider mites present on them. A presence/absence system is used

#### Figure 2.

Examples of (a) and (b) stippling injury to strawberry leaves and (c) spider mite webbing (photo credits: (a) and (b) T.W. Nyoike, UF; and (c) E.M. Rhodes, UF).

Management of Strawberry Insect and Mite Pests in Greenhouse and Field Crops DOI: http://dx.doi.org/10.5772/intechopen.82069

sometimes on large fields but this assessment method has some limitations and a history of mite population in the field is sometimes needed to improve its accuracy. A common threshold for this type of monitoring is 5% of leaves infested. In California, the treatment threshold is an average of 5 mites per leaf before the harvest period begins, which increases to an average of 15–20 mites per leaf once the harvest period begins [7]. An average of 10 spider mites per leaf is a common threshold used in Florida production [8].

There are a number of miticides available for twospotted spider mite management. Thorough spray coverage is essential for effective applications [3]. Rotating modes of action is also very important as spider mites can quickly develop resistance to miticides due to their short life cycle.

There are several commercially available predatory mite species that can be used in a twospotted spider mite management program [3]. They are especially effective in greenhouse settings. Neoseiulus californicus (McGregor) and Phytoseiulus persimilis Athias-Henriot are two commonly used species [9, 10]. Neoseiulus californicus mites (Figure 3) are orange to peach in color and slightly larger than twospotted spider mites. Their eggs are milky white and ovoid in shape. They prefer spider mites as prey and can subsist on other food sources, such as small insects and pollen, when twospotted spider mite numbers are low. For this reason, preventative releases of small numbers of N. californicus early in the season can reduce the severity of mite outbreaks and even eliminate them all together in some cases. In contrast, P. persimilis mites (Figure 4) specialize on spider mites, so their population declines rapidly once the spider mite population has declined to low levels. This can necessitate multiple releases in a season. Adults are pink in color with spider-like legs. Eggs are similar in shape to N. californicus eggs and have a pinkish to orangish tint. Preventative and curative rates are listed on supplier websites. If spider mite numbers are high, it is advisable to knock down the population with a miticide before predatory mites are released. Predatory mites should be released 7–10 days after the miticide application.

#### 3.2 Cyclamen mite

only a short time before entering a resting state prior to molting to the next stage [4]. Females are larger and rounder than males. Development from egg to mature adult takes an average of 19 days, although this time can be as short as 5 days [4]. Optimal conditions for development are high temperatures (up to 38°C) and low

Strawberry - Pre- and Post-Harvest Management Techniques for Higher Fruit Quality

During feeding, twospotted spider mites puncture leaf cells and suck out their contents [3]. The feeding injury causes affected leaves to have a stippled appearance (Figure 2a and b). Spider mites do produce webbing, which is where their common name originates from (Figure 2c). The webbing provides protection from predators and may also help maintain favorable temperature and humidity conditions for the mites. Webbing is only visible when populations are high and, therefore, economic

Monitoring can be accomplished by checking and counting twospotted spider mites on the underside of strawberry leaves with a 10x hand lens [3]. Alternatively, strawberry leaves can be collected from the field and examined later. Leaf samples should be processed within 3 days of collection if possible. In annual production, sampling for twospotted spider mites should begin after the transplants have become established. In perennial culture, sampling should start once the new leaves fully open in the Spring. Sample 13–25 fully mature leaves per hectare. Counting the number of spider mites on each leaf will give more accurate results, but it can be time consuming. An alternative is simply to note how many leaves have spider mites present on them. A presence/absence system is used

Examples of (a) and (b) stippling injury to strawberry leaves and (c) spider mite webbing (photo credits: (a)

humidity [5, 6].

Figure 2.

104

and (b) T.W. Nyoike, UF; and (c) E.M. Rhodes, UF).

damage to the crop is already occurring.

Cyclamen mites, Phytonemus pallidus (Banks), are half the size of spider mites, 0.25 mm, and invisible to the naked eye [3, 7]. Adults are shiny and pinkish to orangish in color while immatures are opaque white. Eggs are ovoid and translucent. They feed on developing tissues and are most commonly found on unfolded

becomes streaks on the leaves that can cover the entire leaf surface and lead to leaf deformation. Heavy infestations can cause stunting of entire plants. Infestations early in the season when strawberry plants are small and have only a few leaves

Management of Strawberry Insect and Mite Pests in Greenhouse and Field Crops

Scouting for Chili thrips is best accomplished by looking for the injury they cause [12]. Leaves with the characteristic injury described above can be gently tapped over a white sheet of paper. This will dislodge any Chili thrips present, which will resemble tiny, yellow dashes crawling on the piece of paper. Thresholds

The predatory mite Amblyseius swirskii (Athias-Henriot) has shown some efficacy against thrips species in vegetable systems [14]. These predators feed primarily on eggs and immatures of thrips. This predatory mite is commercially available and has the potential to be used in other crops like strawberry. Insecticides should be avoided when possible because they cause disruption in the predator complex and cause thrips population to flare up. Insecticides should only be applied if the infes-

There are four species of aphids (Figure 6) commonly found in strawberries: the green peach aphid, Myzus persicae (Sulzer), the melon aphid, Aphis gossypii Glover, the potato aphid, Macrosiphum euphorbiae (Thomas), and the strawberry aphid, Chaetosiphon fragaefolii (Cockerell) [3, 7]. The strawberry aphid can severely affect yield because it transmits a host of virus including the strawberry mild yellow edge virus, strawberry crinkle virus and the strawberry mottle virus [7, 15]. In general, aphids are small (2.54 cm), globular, pear-shaped, soft-bodies insects found on the underside of leaves. Aphids are often various shades of green or yellow but can be black or even pink. There are winged and wingless forms. Aphids can be distinguished from similar insects by the two cornicles (tube-like structures) protruding

Winged females enter fields from nearby infested crops or weedy areas [3, 7]. They can also enter greenhouses. Female aphids can produce daughters without mating, so populations can build up very quickly. Aphids use their sucking mouthparts to feed on plant juices and excrete excess sugar as a sticky, sugary honeydew. Sooty mold fungus will grow on the honeydew and can contaminate fruit. Aphids efficiently transmit plant viruses. In strawberry production, these viruses are mainly a concern in nursery production. Viruses can also persist from one season to

another in perennial production, but this is a rare occurrence.

tation is severe, particularly if thrips numbers are high early in the season.

cause the most damage.

DOI: http://dx.doi.org/10.5772/intechopen.82069

have not yet been developed.

from the end of the abdomen.

3.4 Aphids

Figure 6.

107

Aphids on a grape leaf (photo credit: B. Achhami, UF).

#### Figure 4.

P. persimilis (a) adult and (b) eggs with twospotted spider mites and eggs on a strawberry leaf (photo credit: E. M. Rhodes, UF).

leaves near the midvein and in flower buds. Infested leaves are small and wrinkled. High infestations can cause a compact mass of these leaves in the center of plants. Injury to leaves causes them to turn brown, wither, and die. Any fruit produced is stunted and russety.

Cyclamen mites can persist in perennial production systems, making them a greater threat to these systems [3]. They often come into a field on infested transplants and can also be transported by insects, birds, and even people via contaminated clothes or equipment. The threshold is low, 1 mite per 10 leaves in California [7]. Miticides must be applied in large volumes of water, 2839–4732 liters per hectare, to ensure soaking of the developing tissues in the crown.
