Fall armyworms on target: management strategies for fall armyworm in corn

Corn crop productivity is defined based on productivity factors, which are divided into productivity builders and productivity protectors. With regard to productivity protectors, phytosanitary management (of weeds, diseases and pests) must ensure that these phytosanitary aspects do not negatively interfere with the production potential established based on genetics and the environment. It is currently clear that pest control in corn crops, especially fall armyworm (Spodoptera frugiperda), is one of the practices that presents management difficulties.

 The cartridge caterpillar (Spodoptera frugiperda) belongs to the order Lepidoptera, family Noctuidae. The total cycle of the fall armyworm varies from 24 days to 45 days, being divided into the adult stage (moth, 10 days to 12 days), eggs (3 days to 5 days), neonatal caterpillars (cannibalized until one or two remain per plant). Caterpillars have 6 stages (14 days to 22 days) and end their cycle as pupa, in the soil (7 days to 13 days). Each female has a mass laying that varies from 100 eggs to 150 eggs per laying, and during the cycle it reaches 1000 eggs, being placed preferentially in  The fall armyworm, in high infestations, causes losses that can vary from 20% to 50% , being the main pest of corn crops. In sweet corn, damage can reach 60% (Cruz, 1997) and the degree of damage to the crop is mainly related to the sowing time, climate, nutritional status of the crop and phenological stage of the plant. The critical period of the attack comprises the stages between V2 and V10. A severe attack between V2/V3 in plants causes delays in the initial development, establishment and even death of plants. In this case, there are reductions in the plant stand in the crop. The reduction in leaf area and consequently photosynthetic rate during this period, decisively affects the productivity of the corn crop, as from V4 to V6 the productive potential of the crop is defined. In V8, the number of rows is being defined and between V10 and V12, the length of the cob. The fall armyworm can behave similarly to the elasm caterpillar and the thread caterpillar, in which the larva enters through the base of the plant and feeds on the inside of the stem, causing the symptom known as “dead heart”. This will verify the total or partial sectioning of the plant. However, this is caused by more developed caterpillars. Furthermore, damage has already been seen to the tassel and ear.

The lifestyle habits of the fall armyworm also influence it to be a difficult pest to control. The place where the insect lives is very important. Soon after the eggs hatch, the pest scrapes the corn leaves, but when the instars are exchanged, it moves to the cartridge, where it is more protected from predators, thus also making insecticide management more difficult. In hotter and drier periods (sowings in December and January, for the southern states) the damage caused by the caterpillar is more severe due to higher temperatures, a reduction in the life cycle and more favorable ecological conditions for its development.

Possible management in relation to fall armyworm involves cultural management that must be observed with sowings being carried out at the beginning of the recommended period. In addition, priority should be given to crop rotation with legumes, monitoring with sex pheromone traps, as well as the use of biological control. In this case, caterpillar predators can be mentioned (beetles from the Carabidae family, reduviid bugs and earwigs); egg predators (earwigs); caterpillar parasitoids (young forms of Ichneumonidae, Bracconidae and family flies Tachinidae), egg parasitoids (Trichograma spp.) and entomopathogenic microorganisms (fungi: Nomureae sp., is Beuaveria sp. It's virus: spodoptera baculovirus).

Currently, transgenic corn hybrids are being offered that have the ability to not be attractive for consumption to many pests or even tolerant. In addition to crop rotation and hybrids (with distinct transgenic characteristics).

Another option is the use of chemical control, however this method must consider monitoring fall armyworm damage to the plant. It is considered that the level of economic damage is 10% of the attacked plants (leaves scraped off), so chemical intervention must be carried out. The main groups of insecticides for controlling fall armyworm in off-season corn are carbamates (carbaryl, methomyl and thiodicarb), inhibitors of chitin synthesis (lufenuron, diflubenzuron, triflumuron, novaluron and chlorfuazuron), and spinosins (spinosad), organophosphates (triazophos, trichlorfon and methyl parathion) and pyrethroids (permethrin and lambdacyhalothrin) can eventually be used, however there is evidence of loss of their effectiveness (FMS - Barros, 2012). If early attack occurs on the plants in order to reduce the stand, the spray jet must be directed to the base of the plants, giving preference to nighttime applications with a high volume of spray (200L/ha) using the jet nozzle plane (fan).

Integrated insect management must be carried out to prevent pest insect populations from becoming problems. The use of systemic insecticides in seed treatment should be considered, as it is a localized operation, being an efficient and economical method. However, this method is only efficient as long as the active ingredient in the chemical is active, which on average provides protection for up to the first 18 days after sowing. After this period, monitoring with periodic sampling should be carried out using spraying. Sampling can be carried out in a zigzag pattern or along a perimeter in the field. When entering the field, you must travel at least 30 meters from the entrance (edge ​​or head) of the field and sample 20 plants that are distant from each other. The number of points evaluated is five, with 20 plants per sample, totaling 100 plants.

            Damage is verified by cutting the plants or reducing the leaf area. In the first case, in which it is found that fall armyworms are causing cuts to the seedlings/plants, the control level must be 2%-3% of the attacked plants, as this attack will have direct repercussions on the crop stand and consequently on the number of ears. As for the level of control for leaf attack, the period that requires the most attention should be between V2/V3 and V10. In the first stages (V3 to V4 – approximately 30 days), when 20% of the plants are attacked, a control measure must be taken. However, in later stages V7/V8 (40 days to 60 days) the percentage of attacked plants should be 10%, based on Embrapa recommendations. The time of development of the corn crop must also be considered; in periods of delayed sowing (“safrinha”), 10% of the attacked plants must be taken as a control level (Cruz, 1999). Other parameters that can be adopted indicate that in commercial crops or with Bt technology, they must be managed with insecticide when 17% of the plants have lesions up to 1,3 cm long on new or already expanded leaves (level 3 or higher on the Davis Scale). . After initial management, or in historical conditions of high insect pressure or in environmental circumstances in which the pest cycle is reduced, the damage level that must be adopted is 10%.

            Crop monitoring is essential. To this end, it is recommended to carry out a damage survey from the first stages. The damage level can be defined more specifically, considering the Davis Scale. The survey is carried out by plot (uniform area) considered uniform. 20 plants are evaluated individually, assigning scores to each plant. If scores equal to or above 4 (three) are observed in 3 of these plants, a control measure must be carried out.

            The use of refuge is essential in all crops that have some level of transgenics associated with the fight against fall armyworm. It must be considered that the plants do not Bt they must be located no more than 800m away from transgenic crops. Furthermore, these plots can be sown in different configurations, on the perimeter of the crop, in strips or within the cultivation area. The refuge area must be 10% of the total area.

In two areas of UFSM, experiments were carried out with different corn hybrids following the technical guidelines for corn cultivation (Indicações Técnicas Milho, 2013). In experiment I, two applications of insecticides V3 and V5 were carried out, in experiment II, no insecticides were applied. In each experimental unit, five plants were evaluated using the Davis scale (Davis et al., 1992), which considers a visual scale as shown in figures 1, 2 and 3. And from these evaluations, different degrees of damage to the hybrids, assisting decision making (Table 1). From table 1, it can be seen that corn hybrids that have lower associated grades have a lower fall armyworm attack, which is favorable within an integrated system for the protection of these plants. Hybrids that have scores above 3 require the application of insecticides to control the damage caused by the fall armyworm, thus preventing the plants from reaching high levels as shown in figure 3.

  

 

Table 1. Average scores attributed to hybrids, according to the Davis scale and classification.

Experiment I	Experiment II
Hybrids	Notes	Clas.	Hybrids	Notes	Clas.
Defender 7617 Viptera	1,35	d*	VIP3-Status	1,00	e
DKB 290 Pro3	1,90	cd	VT PRO2-DKB 250	1,10	e
32R48 YH	1,95	cd	MIR162-VIP-Feroz	1,10	e
Status 7205	2,05	cd	Power core-DW-2B610	3,10	dc
SX 7331 VIP	2,20	cd	VT PRO3-DKB-240	3,80	c
P1630H	2,35	cd	Optimum-YH-3F53YB	4,50	bc
Forumla 3949	2,80	bc	Herculex-HX-Biogene	5,70	ab
AG 8780 Pro3	2,80	bc	BT11-TLTG-Celeron	6,80	a
30F53YH	2,85	bc	Conventional-Formula	7,10	a
DKB 240 Pro 3	3,00	bc
30F53	3,10	bc
30F53 YHR	3,75	ab
BG7051	3,95	ab
BG 7060	3,95	ab
30B30H	4,10	ab
30B39 HR	4,55	a
P2530	4,70	a
Media	3,02		Media	3,64
CV	44,18		CV	45,14

Experiment I

Experiment II

Hybrids

Notes

Clas.

Hybrids

Notes

Clas.

Defender 7617 Viptera

1,35

d*

VIP3-Status

1,00

e

DKB 290 Pro3

1,90

cd

VT PRO2-DKB 250

1,10

e

32R48 YH

1,95

cd

MIR162-VIP-Feroz

1,10

e

Status 7205

2,05

cd

Power core-DW-2B610

3,10

dc

SX 7331 VIP

2,20

cd

VT PRO3-DKB-240

3,80

c

P1630H

2,35

cd

Optimum-YH-3F53YB

4,50

bc

Forumla 3949

2,80

bc

Herculex-HX-Biogene

5,70

ab

AG 8780 Pro3

2,80

bc

BT11-TLTG-Celeron

6,80

a

30F53YH

2,85

bc

Conventional-Formula

7,10

a

DKB 240 Pro 3

3,00

bc

 

 

 

30F53

3,10

bc

 

 

 

30F53 YHR

3,75

ab

 

 

 

BG7051

3,95

ab

 

 

 

BG 7060

3,95

ab

 

 

 

30B30H

4,10

ab

 

 

 

30B39 HR

4,55

a

 

 

 

P2530

4,70

a

 

 

 

Media

3,02

 

Media

3,64

 

CV

44,18

 

CV

45,14

 

*means followed by different letters differ at a 5% probability of error using the Duncan test.

 

Integrated management includes actions that range from area preparation, correct choice of sowing time depending on fall armyworm pressure, choice of crop monitoring, crop rotation, use of biological control, rotation of insecticide active ingredients and specificity insecticides; use of seed treatment; use of genetically modified hybrids (Bt corn) and use of hybrid rotation with “gene rotation”; weed control-monitoring. This way it will be possible to reduce damage and have grain productivity in accordance with that established by the genetic potential of corn together with environmental and management conditions.

The full article is in issue 191 of Cultivar Grandes Culturas.