Table 2 Summary of techniques successfully used to detect drought and diseases in plants

Quadratic discriminant analysis (QDA)

Wheat (yellow rust)

Avacado (laurel wilt)

[26]

[33]

92%

94%

Decision tree (DT)

Avacado (laurel wilt)

Sugarbeet (cerospora leaf spot)

Sugarbeet (powdery mildew)

Sugarbeet (leaf rust)

[33]

[41]

95%

95%

86%

92%

Multilayer perceptron (MLP)

Wheat (yellow rust)

[27]

98.9/99.4%

H/D

Partial least square regression (PLSR)

 Raw

 Savitsky-Golay 1st derivative

 Savitsky-Golay 2nd derviative

Celery (sclerotinia rot)

[35]

88.92%

88.18%

86.38%

Partial least square regression (PLSR)

 Fishers linear determinant analysis

Wheat (yellow rust)

Wheat (aphid)

Wheat (powdery mildew)

Wheat (powdery mildew)

[36]

[37]

92%

60%

90%

Fishers linear determinant analysis (FLDA)

Wheat (yellow rust)

Wheat (powdery mildew)

[30]

Erosion and dilation

Cucumber (downey mildew)

[31]

Spectral angle mapper (SAM)

Sugarbeet (cerospora leaf spot)

Sugarbeet (powdery mildew)

Sugarbeet (leaf rust)

Wheat (head blight)

[40]

[39]

89.01–98.90%

90.18–97.23%

61.7%

87%

Artificial neural network (ANN)

Sugarbeet (cerospora leaf spot)

Sugarbeet (powdery mildew)

Sugarbeet (leaf rust)

[41]

96%

91%

95%

Support vector machine (SVM)

Sugarbeet (cerospora leaf spot)

Sugarbeet (powdery mildew)

Sugarbeet (leaf rust)

Barley (drought)

[41]

[45]

97%

93%

93%

10 days before visible signs

Spectral information divergence (SID)

Grapefruit (cankerous, normal, greasy spot. Insect damage, melanose, scab, wind scar)

[38]

95.2%

Simplex volume maximisation

SiVM with DAR

Barley (drought)

Barley (drought)

[44]

[47]

4 days before Vegetation Indices

1.5wk Before  visible signs

LSSVM

Wheat (drought)

[46]

86.6%(H)/76.3%(S)