Kehilangan hasil dan cara pengukurannya Ambang ekonomi
Pemantauan Perkembangan OPT • Pengamatan terhadap kemunculan suatu OPT di suatu wilayah perlu di monitor dari waktu ke waktu dengan interval tertentu tergantung : tingkat tumbuh, jenis tanaman, daur hidup OPT yang diamati, tujuan pengambilan sampel, faktor cuaca, dll. • Pengamatan dilakukan pada sampel tanaman yang dipilih mengikuti ketentuan secara acak atau secara sistematik
Pengngambilan sampel pengamatan Acak Bukan sampel Sampel pengamatan
Pengambilan sampel secara Sistematis rbagai bisa mengikuti Berbagai pola, misalnya sigsaz, Pola huruf X, pola melingkar dsb
Sistematis
Pengukuran Kerusakan karena OPT • Tingkat kerusakan tanaman akibat hama dikenal dengan intensitas serangan atau intensitas kerusakan, • Besarnya intensitas serangan dinyatakan dengan persen.
• Untuk tanaman yang bernilai ekonomi tinggi dan kerusakan yang terjadi bersifat fatal atau sistemik menghancurkan produknya maka perhitungan kerusakan dilakukan dengan rumus • I = n/N x 100 I : intensitas serangan OPT n : Jumlah tanaman yang terserang N : jumlah total sampel tanaman yang diamati
Tanaman dengan kerusakan yang dapat diperkiraan dengan skor atau nilai numerik, contoh: Skor
% Kerusakan
Keterangan (misalnya utk bercak daun)
0
0
Tidak ada yg rusak
1
< (=) 10
Luas bercak daun selebar ± 10% dari helaian daun
2
10 - 20
Luas bercak daun selebar 10-20 % dari helaian daun
3
20 - 40
Luas bercak daun selebar 20 - 40 % dari helaian daun
4
40 - 70
Luas bercak daun selebar 40-70 % dari helaian daun
5
> 70
Luas bercak daun selebar > 70 % dari helaian daun atau tanaman mati
Contoh Skor 1
0
2
3
10% 0%
5%
4
40%
5
70%
!00 %
Skoring terhadap gejala layu 0
1
0 : tdk bergejala 1 : 1-2 daun layu 2 : 3 -4 daun layu 3 : 5 – 7 daun layu
2
3
4
4 : 8 – 15 daun layu 5 : > 15 daun layu / tanaman mati
5
Pengamatan sampel dengan skoring pada suatu hamparan lahan
5
1 4 3 2
3
1 1 5 3 2
2 5 4
Rumus Perhitungan Intensitas Serangan : • I = nixvi / N Z ni : jumlah sampel pada katagori kerusakan Vi : skor pada sampel N : Jumlah total sampel Z : skor tertinggi dari katagori serangan Berdasarkan tabel di atas (6 katagori) pengamatan terhadap misalnya 10 sampel I = 1x1 + 3x2 + 3x3 + 3x5 / 10 x 5 x 100% I = 31/50 x 100%
Economic damage, economic injury level, and economic threshold • Pest management is considered on the ecological and economical thresholds • Ecological consideration is decided on the analysis that the pest control does not harmful to the environment • Economical consideration is decided on the analysis that the pest control gives economical benefit
Economic damage, economic injury level, and economic threshold • Economic damage : the amount of injury which will justify the cost of artificial control measures • Economic Injury Level (EIL) : the lowest population density that will cause economic damage. • Economic threshold : The maximum pest population that can be tolerated at a particular time and place without a resultant economic crop lost, the population density at which control action should be determined (initiated) to prevent an increasing pest population (injury) from reaching the economic injury level.
A pest damage curve (thick line) and associated cost of pest control (thin line) used to estimate at economic injury level (EIL).
This damage curve can take several forms 1. Tolerance or overcompensation phase no yield response 2. Positive yield response to injury 3. Linearity phase e.g., yield loss = -a (unit injury) + b), 4. Desensitization and an inherent impunity phase decreasing 5 No additional yield loss per unit injury.
• The curve can be used with various methods to determine whether or not any action or pest management tactic (e.g., pesticide, biological control, cultural control, etc.) is needed to reduce the damage associated with this pest. • This relationship is uniquely characterized by a critical point, the economic injury level (EIL), or the point in the agricultural production system where the costs associated with pest management equal the benefits from the pest management actions
• Below the pest population represented by the EIL there is no need to take pest control actions because they are not economically justified, but economic damage can occur when the pest population densities are above the EIL.
Pedigo et al • • • • • •
EIL = C/VDIK C = management cost per production unit, V = market value per production unit, D = damage per unit injury, I = injury per pest equivalent, and K = proportional reduction in injury with management Later combined D+I into a single variable, D‟ = percent yield loss per pest.
Variation formula with the assumption of 100% control:
• • • •
EIL = (C x N) / (V x I), N = the number of pests causing injury, I = the percent yield loss (similar to the D‟ value above). V = market value per production unit C = management cost per production unit
Example • In using the EIL = C/VD‟K formula, • if a seasonal average of one insect/plant causes a 10% reduction in yield, • the market value of the crop is $0.4/lb fruit • and you expect 5 lb fruit/plant yield, the cost of control is $0.04/plant, and you can count on a 75% reduction in damage with the control tactic used, then: • EIL = $0.04 cost per plant/($0.4/lb x 0.5 lb/insect x 0.75) = 0.27 insects/plant
• Notice that if you halve the number of insects required to inflict 10% yield loss, you halve the EIL value. • In contrast, if you double the cost of control you double the EIL value, again balancing the tradeoff between control costs and benefits. • In reality, the EIL value can be difficult to calculate exactly because of the temporal and dynamic nature of pest damage and crop value
A two-level, fixed economic threshold with treated (narrow line), i.e., effectively controlled to stay below the EIL, and untreated (thick line) pest populations
• Example, an early season average of one insect might result in 15% yield while late season results in only 5% yield, so the estimate based on a seasonal mean would not be very precise for a given period during the season. •One way to avoid large seasonal differences is to calculate an early-season and a late-season EIL, for example
EIL1 = C/VD1‟K and EIL2 = C/VD2‟K or EIL1 = $0.04 cost per plant/($0.4/lb x 0.75 lb/insect x 0.75) = 0.18 insects/plant EIL2 = $0.04 cost per plant/($0.4/lb x 0.25 lb/insect x 0.75) = 0.53 insects/plant
Delayed response to a biological control tactic
