Agricultural Weather Fumaca
Rio de Janeiro, Brazil
ET₀, GDD, Frost Risk, Spray Conditions.
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Spray conditions
Spray now — conditions ideal
Next ideal window: Thursday 09:00–20:00
Frost tonight
No frost expected tonight.
Irrigation this week
No irrigation needed — rainfall covers the deficit.
Agro calendar · June 2026
1
2
3
4
09–21h High disease +7.5
5
08–24h +6.2
6
06–10h +5.5
7
+2.2mm +6.8
8
+2.1mm +6.6
9
+2mm +8.4
10
+10.5
11
+7.2
12
+2.5mm +9.2
13
12.0mm +10.8
14
3.8mm +9.2
15
1.4mm +6.5
16
12.2mm +8.0
17
1.3mm +8.5
18
0.7mm +3.6
19
+3.3
20
21
22
23
24
25
26
27
28
29
30
Frost riskSpray windowPrecipitationIrrigation needDisease pressureGDD gain
Soil Temperature
Temperature in the root zone at several depths. 5 cm drives germination; 10–20 cm drives root activity for most annuals; 50 cm is the season-long heat reservoir for perennials.
5 cm germination
17.5°C
14.1 – 19.9°C
10 cm root growth
17.8°C
15.0 – 19.8°C
20 cm root growth
18.3°C
16.3 – 19.6°C
50 cm season reservoir
18.7°C
17.5 – 19.5°C
Growing Degree Days
Growing degree days — accumulated warmth above a crop base temperature. Most crops reach flowering, fruit set or harvest at predictable GDD totals from planting.
Thu
Sat
Mon
Wed
Fri
Sun
Tue
Thu
Fri
Accumulated 197.8117.8 GDU
· +197.8117.8 last 7d
Agro weather reference
Frost risk scale (night low)
> 2°C
None
No frost expected. Safe for tender crops and flowering.
0 to 2°C
Light
Marginal frost. Protect seedlings and blossoms of sensitive species.
−2 to 0°C
Moderate
Frost likely. Cover crops, turn on irrigation if available; tender foliage will be damaged.
−4 to −2°C
Severe
Severe frost. Significant damage to flowers, fruit and young growth across most species.
< −4°C
Hard Freeze
Hard freeze. Widespread damage including woody tissue of cold-hardy species near their lower limit.
Spray condition scale
Ideal
Wind under 8 km/h, humidity 60–80%, ΔT below 6°C, no rain — optimal coverage and uptake.
Good
Acceptable. Slightly higher wind or lower humidity, still efficient with standard droplet size.
Marginal
Drift or evaporation risk. Consider a narrower window, or adjust droplet size and add a drift-reducing adjuvant.
Poor
Significant loss expected from drift, evaporation or imminent rain. Wait for a better window.
Do Not Spray
Do not spray. Wind above threshold, rain within two hours, or ΔT too high — product will fail and may drift off-target.
Disease pressure scale
Low
Unfavourable conditions for infection. Routine monitoring only.
Moderate
Favourable conditions developing. Scout fields and plan a protective spray window.
High
Infection pressure is high. Apply protectant before the next wetting event; add a systemic if symptoms are visible.
Very High
Very high pressure with active infection periods. Curative action recommended; rotate modes of action to avoid resistance.
Glossary
ET₀ — Reference evapotranspiration — the water demand from a well-watered grass surface, in mm/day. Combined with rainfall it gives today's water deficit.
GDD — Growing degree days — accumulated warmth above a crop base temperature. Most crops reach flowering, fruit set or harvest at predictable GDD totals from planting.
Leaf wetness hours — Hours per day that leaf surfaces stay wet from dew or rain. The main trigger for fungal spore germination — long wet periods at mild temperatures drive mildew, botrytis and late blight.
Chill hours — Hours below 7°C during winter dormancy — required by apples, cherries, peaches and grapevines to break bud evenly in spring. Too few means delayed, uneven flowering.
THI — Temperature–humidity index — combines heat and humidity into one number to flag stress in livestock and sensitive crops. Values above 72 start to affect dairy cattle.
Water balance — Precipitation minus evapotranspiration over 7 days. Positive means the soil is gaining water; negative means it is drying out and may need irrigation.
Soil temperature — Temperature in the root zone at several depths. 5 cm drives germination; 10–20 cm drives root activity for most annuals; 50 cm is the season-long heat reservoir for perennials.
Agro weather — frequently asked questions
What is GDD and how do I use it?
GDD counts the warmth accumulated each day above a base temperature your crop needs to grow. Track it from planting or bud break — most crops reach flowering, fruit set or harvest at predictable GDD totals. Use base 5°C for cool-season crops (wheat, peas, apples) and base 10°C for warm-season crops (corn, tomatoes, grapes).
Why does evapotranspiration (ET₀) matter?
ET₀ tells you how much water your field lost to the atmosphere today. Combined with rainfall, it gives you the water deficit: if ET₀ is 5 mm and it rained 1 mm, you are 4 mm short and need to irrigate to avoid stress. It is the foundation of every irrigation schedule.
What does leaf wetness mean for disease?
Most fungal pathogens need liquid water on the leaf to germinate. Long wet periods (more than 8–12 hours) combined with mild temperatures (15–25°C) create ideal conditions for downy mildew, botrytis and late blight. When leaf wetness hours are high here, plan a protective spray before the next rain.
When should I spray, and when should I skip it?
Ideal spray conditions need wind under 10–15 km/h, humidity 50–70%, ΔT below 8°C and no rain expected for at least 2–4 hours. High wind causes drift, low humidity evaporates droplets before they land, and rain washes off product. The calendar above highlights the windows that meet all four criteria.
What are chill hours and why do they matter?
Deciduous fruit trees (apples, cherries, peaches) and grapevines need a minimum number of hours below 7°C during winter dormancy to break bud evenly in spring. Too few chill hours means delayed, uneven flowering and lower yield. Check accumulated chill against your cultivar's requirement in late winter before bud break.
Why four soil temperature depths?
Each depth tells a different story. 5 cm controls seed germination and emergence — below 10°C most seeds will not sprout. 10–20 cm is where most root activity happens for vegetables and cereals. 50 cm reflects the longer-term heat reservoir, warming and cooling slowly and driving perennial root growth.
Data: DWD ICON-D2 / ICON-EU / ICON-Global · ET₀ computed via FAO-56 Penman–Monteith · soil temperatures estimated from air temperature · updated every 3 hours.